Influence of nurse birch and Scots pine seedlings on early aerial development of European beech seedlings in an open-field plantation of Central France

Beech woodland can be restored by direct planting of beech (Fagussylvatica L.) seedlings in abandoned areas, but this methodis generally avoided in forestry because of the growth difficultiesof beech in full-light conditions. This study tested a methodthat consists of planting beech seedlings in full-light conditionswith silver birch (Betula pendula Roth.) or Scots pine (Pinussylvestris L.) as nurse trees. A total of 65 two-year-old beechseedlings surrounded by either 3, 4, 5 or 6 pine or birch seedlingsor without competitors were planted in bare-soil open-fieldconditions in Central France. Tree growth and light availabilitywere monitored at the end of each of the following 3 years,and soil moisture was also measured the last year. At the endof the experiment, aerial biomass measurements were made onthe beeches. Results showed that relative beech growth in termsof diameter was significantly reduced by the local neighbouringtrees and that this reduction was particularly noticeable inthe pine treatments where there was extensive pine seedlingdevelopment. In contrast, relative beech height did not exhibitany significant variations among the treatments. Light availabilitywas decreased by the neighbouring trees, especially in the pinetreatments. Light reduction was more pronounced in the last2 years and in the middle or lower parts of the canopy of thesubject beech. Soil water content was lower under the pine canopiesthan under the birch canopies, and was positively correlatedto beech relative diameter growth. Specific leaf area, height-to-diameterratio and crown length-to-crown width ratio weakly but significantlyincreased with competition from the neighbours. Beech biomasspartitioning was only weakly affected by the treatments. Thisstudy showed that nurse trees tend to reduce beech growth butimprove form although effects remained weak due to the insufficientlength of the experiment. Further studies are also needed toquantify the effects of the neighbourhood on the growth of competitiveherbaceous vegetation and on changes in the microclimatic conditions.     

Assessing forest soil CO(2) efflux: an in situ comparison of four techniques

A dynamic, closed-chamber infrared gas analysis (IRGA) system (DC-1: CIRAS-1, PP-Systems, Hitchin, U.K.) was compared with three other systems for measuring soil CO(2) efflux: the soda lime technique (SL), the eddy correlation technique (EC), and another dynamic, closed-chamber IRGA system (DC-2: LI-6250, Li-Cor, Inc., Lincoln, NE). Among the four systems, the DC-1 systematically gave the highest flux rates. Relative to DC-1, SL, EC and DC-2 underestimated fluxes by 10, 36 and 46%, respectively. These large and systematic differences highlight uncertainties in comparing fluxes from different sites obtained with different techniques. Although the three chamber methods gave different results, the results were well correlated. The SL technique underestimated soil CO(2) fluxes compared with the DC-1 system, but both methods agreed well when the SL data were corrected for the underestimation at higher fluxes, indicating that inter-site comparisons are possible if techniques are properly crosscalibrated. The EC was the only system that was not well correlated with DC-1. Under low light conditions, EC values were similar to DC-1 estimates, but under high light conditions the EC system seriously underestimated soil fluxes. This was probably because of interference by the photosynthetic activity of a moss layer. Although below-canopy EC fluxes are not necessarily well suited for measuring soil CO(2) efflux in natural forest ecosystems, they provide valuable information about understory gas exchange when used in tandem with soil chambers.     

Effects of genotype,harvest year and genotype-by-harvest year interactions on arabinoxylan,endoxylanase activity and endoxylanase inhibitor levels in wheat kernels

The effects of genotype, harvest year and their interaction on the levels of arabinoxylans (AX), endoxylanases and endoxylanase inhibitors in wheat were studied using 14 varieties grown in three successive growing periods with diverse climatological conditions. Relations with more commonly evaluated wheat characteristics such as yield, thousand kernel weight, specific weight, protein level, Hagberg falling number (HFN) and α-amylase activity level were examined. Water extractable arabinoxylan (WE-AX) levels in wheat varied much more than total arabinoxylan (TOT-AX) levels. This variability was mainly genetically determined, but harvest year also had an important effect. Total endoxylanase activity levels varied more than a factor of 20 between the different wheat samples. Endogenous endoxylanases typically accounted for only 10–15% of this activity, while wheat-associated microbial endoxylanases accounted for the remaining 85–90%. However, when preharvest sprouting occurred, the contribution of endogenous endoxylanases could sometimes amount to over 40% of this total activity. Endogenous endoxylanase activity levels were mainly determined by the interaction of genotype and harvest year, while wheat-associated microbial endoxylanase activity levels were predominantly determined by genotype alone. Endogenous and microbial endoxylanase activity levels were strongly correlated, suggesting that wheat varieties which are susceptible to preharvest sprouting are often also susceptible to microbial contamination. The TAXI and XIP-type endoxylanase inhibitor levels varied by a factor of 8 and 1.8, respectively. They were mainly determined by genotype and were rather similar in the different growing periods.     

A model for conjunctive use of groundwater and surface waters for control of irrigation salinity

Changes in the hydrologic balance in many irrigation areas, including those in the Murray Basin, Australia, have resulted in high watertables and salinity problems. However, where suitable aquifers exist, groundwater pumping and subsequent irrigation application after mixing with surface waters (referred to as conjunctive water use) can control salinity and watertable depth and improve productivity of degraded land. In order to assess where conjunctive water use will successfully control salinity, it is necessary to estimate the effects of pumped groundwater salinity on rootzone salinity. A simple steady rate model is derived for this purpose from mass conservation of salt and water. The model enables an estimate to be made of rootzone salinity for any particular salinity level of the groundwater being used in conjunction with surface water; this enables calculation of the required crop salt tolerance to prevent yield reductions. The most important input parameters for the model are groundwater salinity, the annual depth of class A pan evaporation, the annual depth of rainfall, the salinity of irrigation water, and a leaching parameter. For model parameters nominated in this paper, where groundwater salinity reaches 5 dS/m a crop threshold salt tolerance greater than 1.6 dS/m is required to avoid yield reductions. Where groundwater salinity approaches 10 dS/m, a crop threshold tolerance of 3 dS/m is required. Whilst the model derived indicates that rootzone salinity is sensitive to groundwater salinity, rootzone salinity is insensitive to leaching for leaching fractions commonly encountered (0.1 to 0.4). The insensitivity to leaching means that it could be expected that similar yields could be attained on heavy or light textured soils. This insensitivity also implies that there is no yield penalty from increasing the mass of pumped salt by pumping to achieve maximum watertable control in addition to leaching. The model developed is also used to estimate yield reductions expected under conjunctive use, for any particular levels of groundwater salinity and crop salt tolerance.     

Genetic characterization of spontaneous diploid androgenetic wheat and triticale plants

The homozygosity of spontaneous hexaploid plants derived from anther culture was evaluated in wheat and triticale by means of 18 and 22 microsatellite markers, respectively. Most of the spontaneous hexaploid plants were homozygous for all the loci tested and had chromosomes recombining for parental alleles. Only 12% of the spontaneous hexaploid wheat plants, 11% of the artificially doubled wheat plants and 4.4% of the spontaneous hexaploid triticale plants were heterozygous at one to three of the loci studied. This showed that spontaneous hexaploid plants mostly came from normal haploid cells, obtained after meiosis, that underwent spontaneous chromosome doubling. However, first or second division restitution, producing unreduced gametes, cannot be completely excluded to explain the origin of the spontaneous hexaploid plants. Cytomixis, involving only one chromosome, or development of aneuploid trisomic gametes, followed by chromosome doubling for the spontaneous hexaploid plants, or transposition events could also explain some of the results obtained.     

Is low-input management system a good selection environment to screen winter wheat genotypes adapted to organic farming?

The move toward resilient and productive agriculture requires, among other innovations, the design of new sustainable farming systems in which the variety plays a main role. Plant breeding strategies adapted to organic farming conditions have to deal with limiting factors. Whereas in north-west France, it is known that trials carried out under high-input management do not give a good prediction of genotype performance in organic conditions, less is known about the relative stability of wheat genotypes between low-input (LI) and organic cropping systems. A retrospective analysis of 34 winter wheat trials conducted from 2004 to 2011 was performed to determine whether data obtained on genotypes grown under LI conditions can be used to predict genotype performance in organic (ORG) target conditions. Every year, ORG and LI (no fungicide or growth regulators, N balance sheet-60 kgN/ha, weed control with herbicides) trials including 25–30 genotypes describing a large range of genetic diversity were sown in three different agro-climatic regions across north-west France. Genotype performance in ORG management system was reduced from 25 to 40 % for yield and from 10 to 22 % for grain protein content. Estimates of genotypic values appeared to be more precise under LI than ORG conditions. Because of high genetic correlations between LI and ORG conditions, the relative efficiency of indirect selection from LI to ORG conditions was approximately 1. Spearman’s rank correlations were high (Rs = 0.54–0.92) and genotype rank inversions generally had a minor extent. However, in 2005 and 2010, almost 50 % of the lines had to be retained in LI to keep 80 % of the top 20 % of genotypes in organic conditions. Compared with previous results from high-input conditions, LI management provided a better prediction of genotype performance under ORG conditions but crossover genotype × management interactions could be observed between both systems. Overall, combining information provided from both LI and ORG crop management systems appears to be a good process for building efficient and adapted breeding schemes for ORG farming conditions.