Environmental and plant-based controls of water use in a Mediterranean oak stand

In this work, new information is reported on water relations of the Mediterranean oak species Quercus pyrenaica based on environmental and physiological measurements carried out during the growing seasons of 2006 and 2007. The interest in this species has increased due to its use in reforestation programs and its impacts on the water resources due to the extensive spontaneous afforestation after the abandonment of forest (firewood, charcoal, livestock, etc.) and agricultural activities, in general in some areas in the Mediterranean region and in particular, in the studied area (Sistema Central range, Spain). The objectives were to evaluate the long-term water use of this stand and its limit and to analyse the specific traits to cope with summer drought, especially the use of stem water storage and deep soil water reserves. Tree water stress associated with depletion of soil water reserves was not observed since the oak trees appeared to avoid a marked water stress using water reserves from deeper soil layers as summer drought progresses. The contribution of mean daily stem water storage to transpiration was low (4%), although it could be greater under dryer conditions. Only at the end of summer of 2006, the transpiration and canopy conductance were reduced due to soil drought. Despite the absence of marked water stress an upper limit was found in transpiration (slightly higher than 3 mm day⁻¹). The heavy use of soil water resources by this species (75% of available soil water in this study) should be considered when evaluating the impact of spontaneous afforestation and reforestation programs on water resources.     

Variation in carbon concentration and basic density along stems of sessile oak (Quercus petraea (Matt.) Liebl.) and Pyrenean oak (Quercus pyrenaica Willd.) in the Cantabrian Range (NW Spain)

Context

Information about variations in basic density (BD) and carbon content (%C) along tree stems is key to assessing forest carbon sinks.

Aims

The aim of the study was to determine any differences in %C and BD between different woody tissues (bark, sapwood and heartwood) in two widespread European oak species (Quercus pyrenaica and Quercus petraea).

Methods

Twenty trees were felled in northern Spain, and 317 discs cut from the trees were dried and analysed to determine %C and BD.

Results

There were significant differences in %C between bark, heartwood and sapwood, and between species. There were also significant differences in BD between the tissues (heartwood?>?sapwood?>?bark), and the BD was higher in Q. petraea than in Q. pyrenaica. Both %C and BD varied along the stem.

Conclusion

More accurate estimates of carbon contents were obtained by using specific values for different heights and anatomical parts, than by using single values.     

Volatile composition analysis by solid-phase microextraction applied to oak wood used in cooperage (Quercus pyrenaica and Quercus petraea): effect of botanical species and toasting process

The purpose of this study was to investigate the sorption of selected volatile substances from oak wood-chip samples (Quercus pyrenaica Willd. and Quercus petraea L.) subjected to different toasting levels, namely, without toasting, with medium toasting, and with strong toasting, through the use of solid-phase microextraction (SPME). The main volatile compounds identified as a function of the toasting level and botanical species were furfural, hexanal, α-pinene, d-limonene, decanal, vitispirane, ethyl hexanoate, cis-3-methyl-γ-octalactone (“oak lactone” or “whisky lactone”), α-terpineol, p-xylene, and nonanal. Considering the data obtained from the toasted woods (medium and strong intensity) in comparison with those of nontoasted woods, it can be pointed out that the average peak area and the number of compounds identified in the gas chromatogram decreased during the toasting process. In general, regarding the compounds analyzed, quantitative differences were found between the two oak wood species under study. High values of volatile compounds were found in Quercus pyrenaica oak wood chips. In addition, for the number of compounds identified in oak wood extracts and directly extracted from solid oak wood chips by SPME, it is concluded that the best extraction process for volatile compounds from oak wood is the use of oak wood-chip liquid extracts.     

土壤温度和水分对长白山3种温带森林土壤呼吸的影响

为了研究土壤温度和土壤含水量对阔叶红松林(山地暗棕壤)、云冷杉暗针叶林(山地棕针叶林土壤)和岳桦林(生草森林土)的土壤呼吸的影响,于2001年9月在长白山进行了土壤实验。利用增加土壤样柱的含水量,将土壤含水量分为9%,、21%、30%、37%和43%5个等级,土壤样品分别在0、5、15、25和35的温度下保持24小时。阔叶红松林土壤在0~35范围内,土壤呼吸速率与温度呈正相关。在一定的含水量范围内(21%~37%),土壤呼吸随含水量的增加而升高,当含水量超出该范围,土壤呼吸速率则随含水量的变化而降低。土壤温度和水分对土壤呼吸作用存在明显的交互作用。不同森林类型土壤呼吸作用强弱存在显著差异,大小顺序为阔叶红松林>岳桦林>云冷杉暗针叶林.红松阔叶林土壤呼吸作用的最佳条件是土壤温度35,含水量37%;云冷杉暗针叶林下的山地棕色针叶土壤呼吸作用的最佳条件是25,21%;岳桦林土壤呼吸作用的最佳条件是35,含水量37%。但是,由于长白山阔叶红松林,云冷杉林和岳桦林处在不同的海拔带上,同期不同森林类型土壤温度各不相同,相差4~5,所以野外所测的同期的山地棕色针叶林土呼吸速率应低于暗棕色森林土呼吸速率,山地生草森林土呼吸速率应高于山地棕色针叶林土的呼吸速率。图2表1参25。     

锐齿栎林土壤呼吸对土壤水热变化的响应

按照5个土壤含水量(0.20、0.25、0.30、0.35、0.40 kg·kg-1)和5个温度(15、20、25、30、35 ℃)梯度设计试验,对取自北亚热带-暖温带过渡区锐齿栎(Quercus aliena var. acuteserrata)天然林中0～20 cm的原状土柱进行恒温培养和呼吸速率测定.结果表明:土壤温度、含水量及二者的交互作用都对土壤呼吸速率产生显著影响(P＜0.01); 土壤呼吸速率与土壤温度呈正相关,随土壤含水量增高的变化规律为单峰曲线,含水量为0.20～0.35 kg·kg-1 时土壤呼吸速率随含水量的增加而增加,0.35 kg·kg-1时土壤呼吸速率最高,0.35～0.40 kg·kg-1时随含水量的增加土壤呼吸速率下降,是对土壤呼吸产生抑制的土壤含水量临界点;锐齿栎林土壤呼吸Q10值的变化范围为1.36～3.10,平均为2.13,Q10随土壤温度的升高而下降,随含水量增加的变化趋势与土壤呼吸速率一致;土壤含水量0.35 kg·kg-1和土壤温度35 ℃结合下的土壤呼吸速率最高; 回归关系表明土壤呼吸速率与土壤温度呈显著的指数函数关系(P＜0.01),与土壤含水量呈二次函数关系(P＜0.10),土壤温度与含水量可以分别解释呼吸速率变化的73.26%与21.85%,共同解释能力为86.40%,土壤温度对呼吸速率的影响大于土壤含水量.     

Dieback of cork oak (Quercus suber) in Catalonia (NE Spain) caused by Botryosphaeria stevensii

Botryosphaeria stevensii Shoemaker (anamorph: Diplodia mutila Fr. apud Mont.) is reported as the cause of canker and dieback of cork oak (Quercus suber L.) in Catalonia (NE Spain). It also causes wilting of trees after cork is removed for industrial purposes. Symptomatology and details of morphology for both anamorph and teleomorph are given.     

Influence of soil organic matter contents on soil water characteristics of forests on east slope of Gongga Mountain

By testing soil organic matter （SOM） contents, soil water contents （SWC） within low suctions, and saturated infiltration rates of samples taken from east slope of Gongga Mountain of China, the enhancive effects of SOM contents on SWC within low suctions and saturated infiltration rates were quantified. The simulated functions might be applied on regional experience forest-hydrology model. The improving function of protecting forest floor and increasing SOM contents on forest ecosystem hydrological effects were also embodied.     

Influence of water stress on susceptibility of red oak (Quercus rubra) to Phytophthora cinnamomi

Influence of water status of oak trees (Quercus rubra) on the development of Phytophthora cinnamomi lesions was studied. On agar media or excised inner bark, growth of P. cinnumomi was reduced by low water potentials. In contrast, on voung saplings or mature oak trees the development of P. cinnamomi lesions was not affected during a period of water stress. But after the end of the water stress treatment, susceptibility of the young saplings to P. cinnamoni increased.     

Impact of stand density on water status and leaf gas exchange in Quercus ilex

Tree thinning reduces tree-to-tree competition and likely contributes to the improvement of tree water status and productivity in water-limited systems. In this study, we examined the importance of competition for water among Quercus ilex trees in open woodlands by comparing the water consumption and physiological status of trees located along stand density gradients which ranged from 10% (low density; LD) to 100% (high density; HD) of canopy cover. The study was carried out at two sites which differed in mean annual rainfall (506 and 816 L m⁻²; D_site and W_site, respectively). Predawn and midday leaf water potential (ψ_d and ψ_m, respectively) and CO₂ assimilation rate (A) were measured every two weeks from mid May to mid September, in eight trees located along a stand density gradient at each site. Sap flow and soil moisture were measured only at D_site. Sap flow was continuously recorded by sap flowmeters (constant heating method) installed in 12 trees along two stand density gradients. Soil moisture (?) was measured every 20 cm for the first meter and then every 50 cm up to 250 cm. Measurements were conducted in 18 soil profiles, 6 located in HD and 12 in LD (six beneath and six out the canopy). At W_site, differences among stand densities for ψ and A were very small and emerged only at the end of the dry season. At D_site, ψ (both predawn and midday), A, ?, and sap flow density were significantly higher in LD trees than in HD ones. At D_site, some water remained unused in the soil at the end of the dry season beyond the canopy in the LD areas, and trees did not experienced such an acute water deficit (ψ_d > −1 MPa) as the HD trees did (ψ_d < −3 MPa). Summer tree transpiration at the stand level (E_stand) tended to saturate with the increase of canopy cover. E_stand increases by 32% when canopy cover goes from 50% to 100%. Results confirmed that the increase of tree-to-tree competition with stand density was much more significant at dry sites. In these sites, tree thinning is recommended as a way to maintain tree functioning.     

Response of Scots pine (Pinus sylvestris L.) and pubescent oak (Quercus pubescens Willd.) to soil and atmospheric water deficits under Mediterranean mountain climate

The physiological responses to water deficits of Scots pine (Pinus sylvestris L.) and pubescent oak (Quercus pubescens Willd.) were studied under Mediterranean mountain climate. Minimum leaf water potentials were ?3.2 MPa for oak and ?2.1 MPa for pine, with higher predawn values for pubescent oak. Relative sap flow declined in both species when vapour pressure deficit (D) went above ca. 1.2 kPa, but stomatal control was stronger for pine during the 2003 summer drought. P. sylvestris plant hydraulic conductance on a half-total leaf area basis (k _L,s?1) was 1.2–2.6 times higher than the values shown by Q. pubescens, and it showed a considerably steeper decrease during summer. Leaf-level gas exchange was positively related to k _L,s?1 in both species. Scots pine was more vulnerable to xylem embolism and closed stomata to prevent substantial conductivity losses. The results of this study confirm that pubescent oak is more resistant to extreme drought events.     

Competition for water in a pecan (Carya illinoensis K. Koch) – cotton (Gossypium hirsutum L.) alley cropping system in the southern United States

Understanding the belowground interactions between trees and crops is critical to successful management of agroforestry systems. In a study of competition for water in an alley cropping system consisting of pecan (Carya illinoensis) and cotton (Gossypium hirsutum) in a sandy loam soil (Rhodic Paleudult) in Jay, Florida, root systems of the two species were separated by trenching to 120 cm depth. A polyethylene barrier was installed in half of the plots. Spatial and temporal variations in soil water content, root distribution and water uptake by both species, and leaf area development and height of cotton were measured. Interspecific competition for water was greater in the non-barrier treatment near tree rows than at the alley center. Competition became evident 3 to 4 weeks after emergence of cotton and increased during the following 7 to 8 weeks. Compared with the non-barrier treatment, the barrier treatment had higher soil water content and better growth of cotton (height, leaf area, and fine root biomass). Cotton lint yield in the barrier treatment (677 kg ha^–1) was similar to that in a sole-crop stand, but higher than in the non-barrier (502 kg ha^–1) treatment. Lint production efficiency of plants was higher in the interior rows in the non-barrier treatment (0.197 kg lint per square meter of leaf area, compared to 0.117 kg in the barrier treatment). The results suggest that trenching or even deep disking parallel to the tree row may reduce competition for water, but the impact on tree growth cannot be established from this study. This revised version was published online in June 2006 with corrections to the Cover Date.     

Measurements of the bioelectrical potential of a Japanese oak (Quercus crispula Blume) sapling: Effect of the radial distribution of inorganic ingredients within a tree stem on the diurnal change in resting potential

This study investigated the relation between the resting potential of a 2-year-old Japanese oak (Quercus crispula Blume) sapling and its physiology, especially the radial transport of water containing inorganic ingredients in the stem using the scanning electron microscope-energy dispersive X-ray microanalyzer (SEM-EDXA) method. The resting potential of a sapling could be monitored continuously with our measuring apparatus. Changes in resting potential were due to the light. The hyperpolarization and depolarization peaks of the resting potential, whose absolute voltage was about 10mV, occurred right after lights-off and lights-on, respectively. The resting potential was found to show periodic responses for each day unit. At night (lights-off), the resting potential tended to depolarize with an increase in tangential strain. On the other hand, during the daytime (lights-on) the resting potential tended to hyperpolarize, depolarize, or show a nearly constant value for the tangential strain. The water containing inorganic ingredients was transported, via transpiration, in both directions between the mature xylem zone and the phloem zone through differentiating xylem cells. This water transport within a tree stem had a significant effect on the diurnal changes in resting potential.Part of this paper was presented at the 47th annual meeting of the Japan Wood Research Society, Kochi, April 3–5, 1997     

Effect of drought on diameter increment of Quercus ilex, Phillyrea latifolia, and Arbutus unedo in a holm oak forest of NE Spain

The present study was carried out to elucidate the drought growth responses of Quercus ilex L., Phillyrea latifolia L., Arbutus unedo L., and other accompanying woody species of the Mediterranean holm oak forest. We submitted holm oak forest stands in Prades mountains (NE Spain) to a 2-year experimental drought. We reduced soil water availability about 15% by plastic strips and funnels that partially excluded rain throughfall and by ditch interception of water runoff. Mean stem diameter increment showed a great variation depending on the species. A. unedo had larger growth rates than Q. ilex and P. latifolia, but it was also the species that experimented the highest growth reduction in the drought plots (77%), suggesting a higher drought sensitivity than Q. ilex (55%) and P. latifolia (no drought effect). The growth reduction was specially marked in the larger trees. Aboveground stand biomass increment, estimated from stem diameter by allometric relationships, was 1.9 Mg ha⁻¹ per year in the control plots. The 15% reduction in the upper soil moisture produced 42% reduction in this biomass increment. In the drier conditions predicted in this Mediterranean area in the frame of climate change, an important reduction of growth rates can be hence expected, accompanied by a gain of dominance of drought-tolerant species such as P. latifolia in detriment of more mesic species such as Q. ilex.     

Underplanting to sustain future stocking of oak (Quercus) in temperate deciduous forests

New Forests - Oaks (Quercus spp.) are one of the most important tree taxa in the northern hemisphere. Although they are dominant in mixed species forests and widely distributed, there are frequent...     

Effects of water state of soil on ecological boundary of leaf Surface ofpopulus davidiana

The effect of water state of soil on eco-boundary over leaf surface was disscussed by takingPopulus davidiana as experimental material. The results show that to change soil water state by some methods was to adjust and control the forming quality of eco-boundary in fact. The plant in good water condition must be accompanied by thinner eco-boundary. This eco-boundary is beneficial to exchange and flow of the substances between plant and environment. Suifenhe Animal and Plant Quarantine Bureau The study was supported by The Chinese Natural Science Foundation, No. 39470136 (Responsible Editor: Chai Ruihai)     

Spatial and temporal variability of soil water in drylands: plant water potential as a diagnostic tool

Arid and semi-arid regions are characterized by low rainfall and high potential evaporative demand. Here, water is the major limiting factor for plant growth and productivity. Soil and surface hydrology properties （e.g. field capacity, infikration rates） effectively control the water re-distribution in the ecosystem, a fact that is aggravated in arid environments. Information of the spatial and temporal accessibility of soil water in desert ecosystems is limited. The purpose of the studies is the application of plant water potential to estimate the spatial and temporal variations of soil water availability in different arid ecosystems of the Negev （Israel） and southern Morocco. As model plants the evergreen shrubs Retama raetam, Thymelaea hirsuta and trees （Acacia tortilis） were chosen. Seasonal and spatial variations of the pre-dawn water potential （ψpd） were examined as diagnostic tool to determine water availability on the landscape level. The seasonal differences in the pre-dawn water potential were less pronounced on the dune compared to the interdune. This showed a better water availability on the dune slope. Also in the investigated wadis systems spatial differences of the water potential could be detected and related to the vegetation pattern.     

Influence of the soil water holding capacity on the potential distribution of forest species. A case study: the potential distribution of cork oak (<Emphasis Type="Italic">Quercus suber</Emphasis> L.) in central-western Spain

This study reports a parametric approach to the climatic and edaphoclimatic potential distribution of the cork oak (Quercus suber L.) in central-western Spain together with an analysis of the influence of the maximum soil water holding capacity (WHC) on such potential distribution. To these ends, we employed 12 climatic and 2 edaphoclimatic parameters of eco-physiological influence derived from the current distribution of cork oaks. The climatic and edaphoclimatic parameters elaborated for two extreme WHC values (50 and 250 mm) are calculated for the whole study area and are mapped by means of a digital elevation model and a geographic information system. The results point to an important climatic potential area for high soil WHC values but there is also a remarkable dependence on this latter parameter, mainly in the Duero basin, since the limits of the climatic potential area are reduced strongly as WHC decreases. We deduce certain other conclusions as regards the importance of this variable in the potential distribution of species and in forestation and reforestation projects using this species.     

Decline and dieback of cork oak(Quercus suber L.) forests in the Mediterranean basin: a case study of Kroumirie,Northwest Tunisia

Assessing the vulnerability of forest ecosystems in the climate change context is a challenging task as the mechanisms that determine this vulnerability cannot be directly observed. Based on the ecological interrelationships between forests and climate, the present review focused on providing current information about vulnerability assessments of cork oak(Quercus suber L.) forests in the Mediterranean basin, especially, in the Kroumirie region(northwest Tunisia), currently under historic extreme drought conditions. From comparing recent findings in this region, we synthesized data on cork oak decline and mortality collected during the historic drought years 1988–1995 period. Climate change impacts cork forest decline, with special interest shown in elevated temperatures and drought; cork oak forest regeneration, and the adaptation of the Kroumirie forest to climate change, are reviewed herein. The studied region has been influenced largely by frequent prolonged drought periods, especially from 1988 to 1995. Droughts were found to consistently have a more detrimental impact on the growth and mortality rates of cork oak populations. Cork oak mortality was recorded for up to 63,622 trees. In the future, more research studies and observational data will be needed, which could represent an important key to understand ecosystem processes, and to facilitate the development of better models that project climate change impacts and vulnerability. The study is useful for researchers and forestry decision makers to develop the appropriate strategies to restore and protect ecosystems, and to help anticipate potential future droughts and climate change.