Effect of nitrogen and phosphorus addition on leaf nutrient concentrations and nutrient resorption efficiency of two dominant alpine grass species

Nitrogen(N)and phosphorus(P)are two essential nutrients that determine plant growth and many nutrient cycling processes.Increasing N and P deposition is an important driver of ecosystem changes.However,in contrast to numerous studies about the impacts of nutrient addition on forests and temperate grasslands,how plant foliar stoichiometry and nutrient resorption respond to N and P addition in alpine grasslands is poorly understood.Therefore,we conducted an N and P addition experiment(involving control,N addition,P addition,and N+P addition)in an alpine grassland on Kunlun Mountains(Xinjiang Uygur Autonomous Region,China)in 2016 and 2017 to investigate the changes in leaf nutrient concentrations(i.e.,leaf N,Leaf P,and leaf N:P ratio)and nutrient resorption efficiency of Seriphidium rhodanthum and Stipa capillata,which are dominant species in this grassland.Results showed that N addition has significant effects on soil inorganic N(NO_(3)^(-)-N and NH_(4)^(+)-N)and leaf N of both species in the study periods.Compared with green leaves,leaf nutrient concentrations and nutrient resorption efficiency in senesced leaves of S.rhodanthum was more sensitive to N addition,whereas N addition influenced leaf N and leaf N:P ratio in green and senesced leaves of S.capillata.N addition did not influence N resorption efficiency of the two species.P addition and N+P addition significantly improved leaf P and had a negative effect on P resorption efficiency of the two species in the study period.These influences on plants can be explained by increasing P availability.The present results illustrated that the two species are more sensitive to P addition than N addition,which implies that P is the major limiting factor in the studied alpine grassland ecosystem.In addition,an interactive effect of N+P addition was only discernable with respect to soil availability,but did not affect plants.Therefore,exploring how nutrient characteristics and resorption response to N and P addition in the alpine grassland is important to understand nutrient use strategy of plants in terrestrial ecosystems.

Deposition of litter and nutrients in leaves and twigs in different plant communities of northeastern Mexico

Studies on litterfall and decomposition provide estimations of decomposition rates of different ecosystems.This is key information to understanding ecosystem dynamics and changes in a scenario of global warming.The objective of this research was to assess litterfall production,the potential deposition of macro and micronutrients through leaf and twig fall as well as macronutrient—use efficiency in three forest ecosystems at different altitudes： a pine forest mixed with deciduous species（S1）; a Quercus spp.forest（S2）; and,a Tamaulipan thornscrub forest（S3）.Total annual litterfall deposition was 594,742 and 533 g m^（-2） for S1,S2 and S3.Leaf litter was higher （68%） than twigs（18%）,reproductive structures（8%） or miscellaneous material（6%）.Micronutrient leaf deposition was higher for Fe followed by Mn,Zn and Cu.Macronutrient leaf deposition was higher for Ca followed by K,Mg and P.Even though P deposition in leaves and twigs was lower than other macronutrients,its nutrient use efficiency was higher than Ca,Mg or K.Altitude and species composition determine litter and nutrient deposition,with higher values at mid-altitudes（550 m）.Altitude is an important factor to consider when analyzing litter production as well as nutrient deposition as shown in this study.Litter production and nutrient deposition are expected to change in a scenario of global warming.

Soil Nutrient Status and Leaf Nutrient Diagnosis in the Main Apple Producing Regions in China

Soil and leaf nutrient analysis are widely used as effective methods of diagnosing nutrient deficiency in fruit trees,the results of which are used to properly manage fertilizer application.Therefore,a survey was conducted for assessment of the soil nutrient status and leaf nutrient concentration in 2 827 apple orchards in the Bohai Bay and Loess Plateau apple production regions of China.The soil organic matter,alkali hydrolyzable N,available P,and available K were 10.91 g·kg^(-1),73.21 mg·kg^(-1),70.22 mg·kg^(-1),and 169.23 mg·kg^(-1)in the Bohai Bay region,respectively,and 11.72 g·kg^(-1),56.46 mg·kg^(-1),14.91 mg·kg^(-1),and 135.78 mg·kg^(-1)in the Loess Plateau region,respectively.Soil organic matter was at a medium-to-low level in both regions,whereas the soil alkali hydrolyzable N was low.In the Bohai Bay region,soil available P was high,but soil available K was deficient.In contrast,both soil available P and K were insufficient in the Loess Plateau region.The Diagnosis and Recommendation Integrated System(DRIS)diagnostic results indicated that the most deficient elements were Ca and K in low-yielding orchards(<35 t·hm(-2))of the Bohai Bay region followed by Fe,N,and Zn;however in the Loess Plateau region,the most deficient elements were P and K followed by N,Zn,and Cu.The findings imply that the application of Ca,K,Fe,N,and Zn fertilizer should be increased in the Bohai Bay region,whereas P,K,N,Zn,and Cu fertilizer should be enhanced in the Loess Plateau region.Meanwhile,use of organic manure is recommended to improve soil quality in the two apple producing regions.