Drought events influence nutrient canopy exchanges and green leaf partitioning during senescence in a deciduous forest

The increase in the frequency and intensity of drought events expected in the coming decades in Western Europe may disturb forest biogeochemical cycles and create nutrient deficiencies in trees.One possible origin of nutrient deficiency is the disturbance of the partitioning of the green leaf pool during the leaf senescence period between resorption,foliar leaching and senesced leaves.However,the effects of drought events on this partitioning and the consequences for the maintenance of tree nutrition are poorly documented.An experiment in a beech forest in Meuse(France)was conducted to assess the effect of drought events on nutrient canopy exchanges and on the partitioning of the green leaf pool during the leaf senescence period.The aim was to identify potential nutritional consequences of droughts for trees.Monitoring nutrient dynamics,including resorption,chemistry of green and senesced leaves,foliar absorption and leaching in mature beech stands from 2012 to 2019 allowed us to compare the nutrient exchanges for three nondry and three dry years(i.e.,with an intense drought event during the growing season).During dry years,we observed a decrease by almost a third of the potassium(K)partitioning to resorption(i.e.resorption efficiency),thus reducing the K reserve in trees for the next growing season.This result suggests that with the increased drought frequency and intensity expected for the coming decades,there will be a risk of potassium deficiency in trees,as already observed in a rainfall exclusion experiment on the same study site.Reduced foliar leaching and higher parititioning to the senesced leaves for K and phosphorus(P)were also observed.In addition,a slight increase in nitrogen(N)resorption efficiency occurred during dry years which is more likely to improve tree nutrition.The calcium(Ca)negative resorption decreased,with no apparent consequence in our study site.Our results show that nutrient exchanges in the canopy and the partitioning of the green leaf pool can be modified by drought events,and may have consequences on tree nutrition.

Nutrients of green and senesced leaves of a Robinia pseudoacacia plantation along a latitudinal gradient on the Loess Plateau,China

Plantations have been widely established to improve ecosystem services and functioning.Black locust,Robinia pseudoacacia L.is a common,widely planted species to control soil erosion on the Loess Plateau.Previous studies have focused on economic values but the interactions between soil and plant carbon(C),nitrogen(N)and phosphorus(P)remain unknown.Investigating variations of soil,green and senesced leaf C,N and P levels in R.pseudoacacia along a latitudinal gradient is useful to understanding its ecological functions.The results show that soil C,N and senesced leaf N and P significantly decreased with an increase in latitude,but there were no significant changes in the senesced leaf C and soil P.The resorption efficiency of N was related with latitude and soil N levels,and the relation between green leaf N and soil N was significant.These relations suggest that soil N was the key in affecting green leaf N levels.At higher latitudes,senesced leaves had lower N levels associated with higher N resorption efficiency to maintain a stable N content in green leaves.With a decrease of soil N,R.pseudoacacia can enhance N resorption efficiency to meet the demand of growth.Thus,it is an important species for reforestation,especially in nutrient-poor environments.

Identification and analysis of differentially expressed genes involved in dark-induced photoperiod response and senescence of soybean leaves by suppression subtractive hybridization

A cDNA subtractive library enriched for dark-induced up-regulated ESTs was constructed by suppression subtractive hybridization(SSH) from leaf tissues of soybean cultivar DongNong L13 treated with short-day(8-h light/16-h dark) and long-day(16-h light/8-h dark) conditions.A total of 148 clones were sequenced,representing 76 unique ESTs which corresponded to about 20% of 738 clones from the cDNA library and showed a significant up-regulation of at least three fold verified by dot blot hybridization.The putative functions of ESTs were predicted by Blastn and Blastx.The 43 differentially expressed genes identified by subtractions were classified according to their putative functions generated by Blast analysis.Genetic functional analysis indicated that putative proteins encoded by these genes were related to diverse functions during organism development,which include biological regulation pathways such as transcription,signal transduction and programmed cell death,protein,nucleic acid and carbohydrate macromolecule degradation,the cell wall modification,primary and secondary metabolism and stress response.Two soybean transcription factors enhanced in SD conditions,GAMYB-binding protein and DNA binding protein RAV cDNAs that may be involved in SD soybean photoperiod response,had been isolated using 5'-and 3'-rapid amplification of cDNA ends(RACE)(Genbank Accession numbers DQ112540 and DQ147914).

N and P resorption in a pioneer shrub(Artemisia halodendron) inhabiting severely desertified lands of Northern China

Nutrient resorption is an important conservation mechanism for plants to overcome nutrient limitation in the less fertile area of desertifled land. In the semi-arid Horqin Sandy Land of Northern China, the shrub Artemisia ha/odendron usually colonizes into the bare ground of severely desertified land as a pioneer species. It is, therefore, expected that A. ha/odendron will be less dependent on current nutrient uptake through efficient and proficient re- sorption of nutrients. In this study, we found that averaged nitrogen （N） and phosphorus （P） concentrations in se- nesced leaves significantly varied from 12.3 and 1.2 mg/g in the shifting sand dune to 15.9 and 1.9 mg/g in the fixed sand dune, respectively, suggesting that foliar N and P resorption of A. ha/odendron were more proficient in the shifting sand dune. In particular, positive relationships between nutrient concentrations in senesced leaves and soil nutrient availability indicate that A. ha/odendron in infertile habitats is more likely to manage with a low level of nu- trients in senesced leaves, giving this species an advantage in infertile soil. Moreover, foliar N- and P-resorption efficiencies and proficiencies showed limited inter-annual variability although annual precipitation varied greatly among 2007-2009. However, N and P resorption of A. ha/oc/endron were not more efficient and proficient than those previously reported for other shrubs, indicating that the pioneer shrub in sand dune environments does not rely more heavily than other plants on the process of resorption to conserve nutrients. Incomplete resorption of nutrients in A. halodendron suggests that senesced-leaf fall would return litter with high quality to the soil, and thereby would indirectly improve soil nutrient availability. The restoration of desertified land, therefore, may be ac- celerated after A. halodendron pioneers into shifting sand dunes.

Proteome analysis of peroxisomes from dark-treated senescent Arabidopsis leaves

Peroxisomes compartmentalize a dynamic suite of biochemical reactions and play a central role in plant metabolism, such as the degradation of hydrogen peroxide, metabolism of fatty acids, photorespiration, and the biosyn- thesis of plant hormones. Plant peroxisomes have been traditionally classified into three major subtypes, and in-depth mass spectrometry （MS）-based proteomics has been per- formed to explore the proteome of the two major subtypes present in green leaves and etiolated seedlings. Here, we carried out a comprehensive proteome analysis of perox- isomes from Arabidopsis leaves given a 48-h dark treatment. Our goal was to determine the proteome of the third major subtype of plant peroxisomes from senescent leaves, and further catalog the plant peroxisomal proteome. We identified a total of 111 peroxisomal proteins and verified the peroxisomal localization for six new proteins with potential roles in fatty acid metabolism and stress response by in vivo targeting analysis. Metabolic pathways compartmentalized in the three major subtypes of peroxisomes were also compared, which revealed a higher number of proteins involved in the detoxification of reactive oxygen species in peroxisomes from senescent leaves. Our study takes an important step towards mapping the full function of plant peroxisomes.

Resorption efficiency of leaf nutrients in woody plants on Mt. Dongling of Beijing, North China

Aims To explore resorption efficiency of nitrogen(NrE)and phosphorus(PrE)of woody plants in relation to soil nutrient availability,climate and evolutionary history,in North China.Methods We measured concentrations of nitrogen([N])and phosphorus([P])in both full expanded mature green and senescent leaves of the same individuals for 88 woody species from 10 sites of mt.Dongling,beijing,China.We built a phylogenetic tree for all these species and compared NrE and PrE among life forms(trees,shrubs and woody lianas)and between functional groups(N-fixers and non-N-fixers).We then explored patterns of NrE and PrE along gradients of mean annual temperature(MAT),soil inorganic N and available P,and phylogeny using a general linear model.Important Findingsmass-based NrE(NrEm)and PrE(PrEm)averaged 57.4 and 61.4%,respectively,with no significant difference among life forms or functional groups.Neither NrEm nor PrEm exhibited significant phylogenetic signals,indicating that NrEm and PrEm were not phylogenetically conserved.NrEm was not related to[N]in green leaves;PrEm was positively correlated with[P]in green leaves;however,this relationship disappeared for different groups.NrEm decreased with[N]in senescent leaves,PrEm decreased with[P]in senescent leaves,for all species combined and for trees and shrubs.NrEm decreased with soil inorganic N for all species and for shrubs;PrEm did not exhibit a significant trend with soil available P for all species or for different plant groups.Neither NrEm nor PrEm was significantly related to MAT for overall species and for species of different groups.