Diversity of leaf unfolding dynamics among tree species: New insights from a study along an altitudinal gradient

Leaf unfolding is a key ecosystem parameter controlling carbon and water fluxes and affecting forest dynamics. This parameter is highly sensitive to temperature and, consequently, often used as an indicator of global change. In this paper, we analyzed weekly leaf unfolding dynamics for seven temperate species (Fagus sylvatica L., Acer opalus Mill., Sorbus aria L., Quercus pubescens Willd. Abies alba Mill., Pinus sylvestris L., Pinus nigra Arnold). The effects of temperature on leaf unfolding were studied in situ using several methods and proxies. First, in a spatial approach, leaf unfolding dates were measured along two altitudinal gradients situated on the north and south face of the Mont Ventoux to test altitudinal and slope effects. Second, in a temporal approach, the year effect was analyzed on the north face by comparing two contrasted years (2006 and 2007). Finally, the role of temperature was investigated directly by linking leaf unfolding patterns and temperatures recorded during the leaf unfolding process itself.Two major conclusions were obtained. First, three distinct leaf unfolding patterns were revealed: a rapid sigmoid pattern for the deciduous species group, a slow kinetic pattern for the pines and an intermediate pattern for A. alba. Second, we found an unexpected pattern of variation in the response to spatial or temporal variation of temperature. The more sensitive a species was to temperature variations between years, the less sensitive it was to temperature variations due to altitude. Finally, we discuss that these results can be correlated to two major life history traits: evergreen vs. deciduous and shade tolerant vs. shade intolerant.     

Phenotypic plasticity of yield and phenology in wheat, sunflower and grapevine

This paper focuses on the interaction between genotype and environment, a critical aspect of plant breeding, from a physiological perspective. We present a theoretical framework largely based on Bradshaw's principles of phenotypic plasticity (Adv. Gen. 13: 115) updated to account for recent developments in physiology and genetics. Against this framework we discuss associations between plasticity of yield and plasticity of phenological development. Plasticity was quantified using linear models of phenotype vs environment for 169 wheat lines grown in 6 environments in Mexico, 32 sunflower hybrids grown in at least 15 environments in Argentina and 7 grapevine varieties grown in at least 14 environments in Australia.In wheat, yield ranged from 0.6 to 7.8 t ha⁻¹ and the range of plasticity was 0.74–1.27 for yield and 0.85–1.17 for time to anthesis. The duration of the post-anthesis period as a fraction of the season was the trait with the largest range of plasticity, i.e. 0.47–1.80. High yield plasticity was an undesirable trait as it was associated with low yield in low-yielding environments. Low yield plasticity and high yield in low-yielding environments were associated with three phenological traits: early anthesis, long duration and low plasticity of post-anthesis development.In sunflower, yield ranged from 0.5 to 4.9 t ha⁻¹ and the range of plasticity was 0.72–1.29 for yield and 0.72–1.22 for time to anthesis. High yield plasticity was a desirable trait as it was primarily associated with high yield in high-yielding environments. High yield plasticity and high yield in high-yielding environments were associated with two phenological traits: late anthesis and high plasticity of time to anthesis.In grapevine, yield ranged from 1.2 to 18.7 t ha⁻¹ and the range of plasticity was 0.79–1.29 for yield, 0.86–1.30 for time of budburst, 0.84–1.18 for flowering, and 0.78–1.16 for veraison. High plasticity of yield was a desirable trait as it was primarily associated with high yield in high-yielding environments. High yield plasticity was associated with two phenological traits: plasticity of budburst and plasticity of anthesis.We report for the first time positive associations between plasticities of yield and phenology in crop species. It is concluded that in addition to phenology per se (i.e. mean time to a phenostage), plasticity of phenological development merits consideration as a distinct trait influencing crop adaptation and yield.     

Shiraz vines maintain yield in response to a 2–4 °C increase in maximum temperature using an open-top heating system at key phenostages

We measured the effects of increased daytime temperature during 2- (2007/08) or 3-week periods (2008/09) on the yield and yield components of irrigated Shiraz vines in the Barossa Valley of Australia. A simple and inexpensive open system was used to elevate temperature during a single phenological window, either bracketing budburst (E-L stage 4), shortly after flowering (E-L stage 23), bracketing pea size (E-L stage 31), around veraison (E-L stage 35) or shortly before harvest (E-L stage 38). Two important features of the heating systems were tracking of diurnal temperature dynamics, and maintaining relative humidity, hence avoiding the interaction between temperature and vapour pressure deficit. Minimum temperature was unchanged.Compared to controls, maximum ambient temperature was increased between 1.8 and 4.1 °C in treated plots but canopy temperature of treated vines only increased by 0.9–1.1 °C. Elevation of bunch temperature was 2.3–3.2 °C. Increasing temperature around budburst transiently accelerated development in comparison to controls; no phenological changes were detected for other timings of treatment. Yield averaged 4.3 kg vine⁻¹ in 2007–08 and 6.1 kg vine⁻¹ in 2008–09. In both seasons and for all timings of treatment, increasing temperature did not affect yield or its components; lack of yield response did not result, therefore, from compensatory mechanisms, e.g. heavier berries compensating for fewer fruit. The dynamics of berry growth and total soluble solids were largely unaffected by temperature. Under our experimental conditions, the capacity of irrigated Shiraz canopies to partially buffer a 2–4 °C increase in maximum ambient temperature may have been important for the maintenance of yield, and berry growth and sugar accumulation.     

Rootstock effect on budburst of ‘Premier’ low-chill peach cultivar

To determine the effect of rootstock with different chilling requirements on the bud break of the low-chill ‘Premier’ peach cultivar (150 CH), the trees grafted on ‘Newbelle’ (150 CH) and ‘O’Henry’ (750 CH) seedling rootstocks were forced in a glasshouse after being subjected to 100, 200 and 300 CU chilling. The percentage of flower bud burst was slightly higher on ‘Newbelle’ than on ‘O’Henry’, although the difference was not significant. There was little leaf bud burst with 100 CU chilling on both rootstocks. With 200 and 300 CU chilling, the percentage of leaf bud burst and the total leaf number per tree was higher on the ‘Newbelle’ than on the ‘O’Henry’ rootstocks.     

Phenology and growth dynamics in Mediterranean evergreen oaks: Effects of environmental conditions and water relations

Budburst date and shoot elongation were measured in two mature Mediterranean evergreen oaks (Quercus suber and Quercus ilex) and their relationships with meteorological and tree water status (predawn leaf water potential) data were analysed. Experimental work took place at two sites: Mitra 2 - Southern Portugal (2002-2003) and Lezirias - Central Portugal (2007-2010). Quercus suber phenology was studied at both sites whereas Q. ilex was only studied at Mitra 2. Quercus suber budburst date occurred at a photoperiod around 13.8 h (± 0.26) - late April/early May - and was highly related to the average daily temperature in the period 25 March - budburst date (ca. 1.5 months prior to budburst), irrespective of site location. In that period, budburst date was much more dependent on average maximum than average minimum daily temperature. Base temperature and thermal time for Q. suber were estimated as 6.2 °C (within the reported literature values) and 323 degree-days, respectively. Q. ilex budburst occurred about 6 weeks earlier than in Q. suber (photoperiod: 12.3 h (±0.3)). Relationships of Q. ilex budburst date and temperature were not studied since only 2 years of data were available for this species. Q. suber shoot elongation underlying mechanisms were quite different in the two sites. At Mitra 2 (Q. suber and Q. ilex), there was a considerable tree water stress during the dry season which restricted shoot elongation. Shoot growth was resumed later in the wet autumn when tree water status recovered again. At the Lezirias site Q. suber water status was not restrictive. Therefore, shoot elongation was mainly dependent on nutrient availability in top soil, as suggested by the strong and positive relationships between annual shoot growth and long-term cumulative rainfall (2-4 months) and short-term average temperature (1 month) prior to budburst. Annual shoot elongation at this well-watered site was higher than in Mitra 2, and variability of growth between trees was enhanced after warm, wet springs when shoot elongation was higher. Results obtained are relevant to the carbon balance, productivity and management of evergreen Mediterranean oak woodlands, particularly under the foreseen climate change scenarios.     

Impact of site and provenance on economic return in Nordmann fir Christmas tree production

Abstract

The economic potential of 35 seed lots from Danish landraces of Nordmann fir [Abies nordmanniana (Stev.) Spach.] and seven imported provenances were evaluated for high-value Christmas tree production over a full rotation at six locations in Denmark. Naturally grown Christmas trees were evaluated and no leader length control or trimming of the side branches was allowed, but only simple cutting of double terminal leaders. Seed source as well as site strongly affected the economic revenue. Average net sales price per planted tree ranged over sites from €2.43 to €6.64, and among provenances from €1.38 to €7.06 with an average of €4.95. Changes in prices and grading as seen under cycling market conditions seemed not to affect the economic ranking of the better part of the provenances, whereas discounting the net sales income caused moderate rank changes, reflecting differences in rotation time. Limited seed source by site interactions were present and mainly caused by the slowest growing sources. Among the Danish domesticated seed sources of mostly unknown origin several were as suitable as the tested imported sources. In general, the Danish sources were faster growing than imports, although very large variation was present.     

Mycorrhizae support oaks growing in a phylogenetically distant neighbourhood

Host-plants may rarely leave their ancestral niche and in which case they tend to be surrounded by phylogenetically distant neighbours. Phylogenetically isolated host-plants might share few mutualists with their neighbours and might suffer from a decrease in mutualist support. In addition host plants leaving their ancestral niche might face a deterioration of their abiotic and biotic environment and might hence need to invest more into mutualist partners. We tested whether phylogenetic isolation of hosts from neighbours decreases or increases abundance and activity of their mutualists and whether mutualist activity may help to compensate deterioration of the environment. We study oak-hosts and their ectomycorrhizal fungi mutualists established in the litter layer formed by the phylogenetically closely or distantly related neighbourhood. We find that oaks surrounded by phylogenetically distant neighbours show increased abundance and enzymatic activity of ectomycorrhizal fungi in the litter. Moreover, oaks surrounded by phylogenetically distant neighbours also show delayed budburst but ectomycorrhizal fungi activity partly compensates this negative effect of phylogenetic isolation. This suggests decreased nutrient availability in a phylogenetically distant litter partly compensated by increased litter-degradation by ectomycorrhizal fungi activity. Most observed effects of phylogenetic isolation cannot be explained by a change in baseline soil fertility (as reflected by nutritional status of fresh oak litter, or soil microbial biomass and activity) nor by simple reduction of percentages of oak neighbours, nor by the presence of gymnosperms. Our results show that colonizing new niche represented by the presence of distantly related neighbours may delay plant phenology but may be supported by mycorrhizal mutualists. Studies on other host-plant species are required to generalize our findings.