Biomass allocation between leaf and stem regulates community-level plant nutrient resorption efficiency response to nitrogen and phosphorus additions in a temperate wetland of Northeast China

Aims Nutrient resorption is a crucial component of plant nutrient use strategy,yet the controls on the responses of community-level nutrient resorption to altered nutrient availability remain unclear.Here,we addressed two questions:(1)Did leaf and stem nutrient resorption respond consistently to increased nutrient availability?(2)Was community-level plant nutrient resorption response after nutrient enrichment driven by the intraspecific plasticity in plant nutrient resorption or by altered species composition?Methods We investigated the changes in aboveground biomass,and leaf and stem nutrient resorption of individual species after 3-year nitrogen(N)and phosphorus(P)additions,and assessed community-level nutrient resorption response to 3-year nutrient additions in a graminoid-dominated temperate wetland,Northeast China.Important Findings For both leaves and stems,N and P additions did not affect nutrient resorption efficiency,but they decreased respective nutrient resorption proficiency.Similarly,community-level N and P resorption proficiency declined with respective nutrient addition.Community-level N and P resorption efficiency was reduced by N addition primarily due to altered community composition and declined leaf:stem ratio.These results suggest that leaf and stem nutrient resorption processes exhibit consistent responses to increasing nutrient availability in the temperate wetland.These findings highlight the importance of altered species composition and biomass allocation between leaf and stem in driving community-level nutrient resorption response to nutrient enrichment.

Lake-level records support a mid-Holocene maximum precipitation in northern China

Lake level and its inferred East Asian summer monsoon(EASM)evolution in northern boundary of EASM during the Holocene are highly debated.Here,we present a 15-ka record of glycerol dialkyl glycerol tetraethers(GDGTs)in a closed lake in northern China to address this issue.Surface and downcore sediment data demonstrate sedimentary GDGT-0 and branched GDGTs(brGDGTs)are of aquatic production.Contents of GDGT-0 and brGDGTs increase but brGDGT-based paleo-temperature proxy decreases with water depth in surface sediments along a nearshore to offshore transect.This trend is likely due to an increasingly hypoxic condition,favored by anaerobic microbes producing these GDGT-0 and brGDGTs,in bottom water.Accordingly,brGDGT-derived water temperature and pH would reflect bottom water conditions that are largely regulated by water depth of the lake.Downcore GDGT data and their derived temperature and pH consistently reveal a gradually increasing lake level from the late Pleistocene to the early Holocene,a high level during 9.5-5 ka BP and a decreasing trend afterward.The lake-level records from independent and robust proxies in this study largely agree with pollen records in the region,supporting a mid-Holocene maximum EASM precipitation.