The Response And Recovery Of Soil Nematode Communities To Extreme Drought In An Alpine Meadow On The Eastern Tibetan Plateau

In recent years,the frequency,duration,and severity of extreme drought events will continue to increase globally due to warming and decreasing precipitation.This trend has been occurring on the eastern Tibetan Plateau.Prolonged extreme drought and its long-lasting legacy effects can disrupt the stability of soil nematode communities and further affect the soil ecosystem functions.Nematodes,a key component of soil food web,play a crucial role in ecosystem functions.Therefore,the nematodes are effective biological indicators of soil ecosystem response to extreme drought events.It is not yet well known how nematode communities respond to and recover from extreme drought.We investigated the response of soil nematode communities to extreme drought and their recovery processes by conducting fieldcontrolled experiments to simulate extreme drought events on the eastern edge of the Tibetan Plateau,and studied the abundance,diversity indices,and ecological function indices of soil nematode communities,as well as the weighted mean body size of the communities to extreme drought.2019-2020,we conducted extreme drought and rewetting of different durations treatments(each treatment was correspondingly matched with a natural rainfall control),and collected soil samples after the treatments to determine soil physiochemical properties,microbial communities,and nematode communities.The main results were as follows:i)Extreme drought significantly suppressed the total nematode abundance and the abundance of trophic and c-p groups,and altered the nematode community composition.In addition,extreme drought significantly suppressed the nematode metabolic footprint and significantly reduced the community-weighted mean body size of plant feeders and fungal feeders.However,extreme drought significantly increased the proportion of r-strategists and fungal feeders,resulting in a nematode channel ratio(NCR)< 0.5.ii)The lag effect of extreme drought still suppressed the nematode abundance,genus richness and diversity indices until 6 weeks after rewetting.The abundance of omnivorous and carnivorous did not recover to the control level during the whole rewetting period,while plant feeders and fungal feeders recovered to the control level at 2 weeks and were higher than the control level at 6 weeks,thus the total abundance of the nematode community fully recovered at 6 weeks.In addition,the long-lasting legacy effect of extreme drought significantly inhibited the recovery of bacterial feeders,but never inhibited fungal feeders,resulting in a decrease in the nematode channel ratio(NCR)and an increase in the channel index(CI).Moreover,the legacy effect of extreme drought strongly suppressed the community-weighted mean(CWM)body size of nematode communities,especially those of fungal and bacterial feeders.iii)Nematode abundance increased nonlinearly with increasing soil moisture content during both extreme drought and rewetting periods,with a different response of each trophic group.During the extreme drought periods,when soil moisture content was low(SM< 25.0%),there was no significant change in the abundance of fungal feeders with increasing moisture content.However,during the rewetting periods,when soil moisture content was low(SM< 22.5%),there was a slight tendency for the abundance of fungal and bacterial feeders to decrease with increasing moisture content.In conclusion,extreme drought severely damaged soil nematode communities with negative long-lasting legacy effects,significantly altering nematode community composition and further affecting nematode-driven ecosystem functions and services.However,soil nematodes can gradually rebuild their communities,resume their metabolic activities,and participate in nutrient cycling and organic decomposition after rewetting.This study focused on the response and recovery of soil nematode community to extreme drought in an alpine meadow on the eastern Tibetan Plateau,which is helpful to monitor and evaluate the health status of the ecosystem,which will have important scientific significance for the protection and restoration of the alpine meadow ecosystem on the Tibetan Plateau.