Drought adaptability of phreatophytes:insight from vertical root distribution in drylands of China

Aims The vertical distribution of plant roots is a comprehensive result of plant adaptation to the environment.Limited knowledge on fine vertical root distributions and complex interactions between roots and environmental variables hinders our ability to reliably predict climatic impacts on vegetation dynamics.This study attempts to understand the drought adaptability of plants in arid areas from the perspective of the relationship between vertical root distribution and surroundings.Methods By analyzing root profiles compiled from published studies,the root vertical profiles of two typical phreatophytes,Tamarix ramosissima and Populus euphratica,and their relationships with environmental factors were investigated.A conceptual model was adopted to link the parameter distribution frequency with plant drought adaptability.Important Findings The strong hydrotropism(groundwater-dependent)and flexible water-use strategy of T.ramosissima and P.euphratica help both species survive in hyperarid climates.The differences in the developmental environments between T.ramosissima and P.euphratica can be explained well by the different distribution characteristics of root profiles.That is,higher root plasticity helps T.ramosissima develop a more efficient water-use strategy and therefore survive in more diverse climatic and soil conditions than P.euphratica.We conclude that the higher variation in root profile characteristics of phreatophytes can have greater root adaptability to the surroundings and thus wider hydrological niches and stronger ecological resilience.The inadequacy of models in describing root plasticity limits the accuracy of predicting the future response of vegetation to climate change,which calls for developing process-based dynamic root schemes in Earth system models.

Root production, mortality and turnover in soil profiles as affected by clipping in a temperate grassland on the Loess Plateau

Aims Clipping or mowing for hay,as a prevalent land-use practice,is considered to be an important component of global change.Root production and turnover in response to clipping have great implications for the plant survival strategy and grassland ecosystem carbon processes.However,our knowledge about the clipping effect on root dynamics is mainly based on root living biomass,and limited by the lack of spatial and temporal observations.The study aim was to investigate the effect of clipping on seasonal variations in root length production and mortality and their distribution patterns in different soil layers in semiarid grassland on the Loess Plateau.Methods Clipping was performed once a year in June to mimic the local spring livestock grazing beginning from 2014.The minirhizotron technique was used to monitor the root production,mortality and turnover rate at various soil depths(0–10,10–20,20–30 and 30–50 cm)in 2014(from 30 May to 29 October)and 2015(from 22 April to 25 October).Soil temperature and moisture in different soil layers were also measured during the study period.Important Findings Our results showed that:(i)Clipping significantly decreased the cumulative root production(P<0.05)and increased the cumulative root mortality and turnover rates of the 0–50 cm soil profile for both years.(ii)Clipping induced an immediate and sharp decrease in root length production and an increase in root length mortality in all soil layers.However,with plant regrowth,root production increased and root mortality decreased gradually,with the root production at a depth of 30–50 cm even exceeding the control in September–October 2014 and April–May 2015.(iii)Clipping mainly reduced root length production and increased root length mortality in the upper 0–20 cm soil profile with rapid root turnover.However,roots at deeper soil layers were either little influenced by clipping or exhibited an opposite trend with slower turnover rate compared with the upper soil profile,leading to the downward transport of root production and living root biomass.These findings indicate that roots in deeper soil layers tend to favour higher root biomass and longer fine root life spans to maximize the water absorption efficiency under environmental stress,and also suggest that short-term clipping would reduce the amount of carbon through fine root litter into the soil,especially in the shallow soil profile.