Impact of climate change-induced drought on tree root hydraulic properties and competition belowground

摘要: Drought has been projected to increase as global warming progresses, putting forest health in jeopardy. Water availability already is a major factor limiting plant growth, especially forests and orchards on shallow, sandy soils or in regions with low precipitation. Furthermore, salinisation of agricultural an increasing problem, often caused by the increased water demand for irrigation drier climates. Research on drought salt resistance strategies of plants classically focussed the dynamics stem leaf water. However, it in the soil where uptake occurs compete and nutrients. Although number studies are addressing belowground traits, better understanding adaptability of tree root systems limitation belowground competition is needed be able predict effects climate change on mature stands woody crops. This study five tree species temperate mixed Mediterranean fruit tree orchards aims at answering important questions influence of reduced moisture competitive interactions structure and function tree systems. In particular, this study were test whether (i) hydraulic conductivity decreases response shortage as does shoot hydraulic conductivity, (ii) fine roots act ‘hydraulic fuses’ the soil-plant-atmosphere continuum, (iii) below-ground competitive ability symmetric directly linked system size, and (iv) ability differs between species and not modified resource availability. showed that: i) Quercus petraea (MATT.) LIEBL. generally responded to moderate severe axial conductivity, while Fagus sylvatica L. mostly did not. The same pattern was found salt-stressed Olea europaea roots, the conductivity which increased salinity. Drought- and/or salt-adapted species such petraea and europea seem capable partly compensating for water shortage-induced biomass losses mechanism rarely observed aboveground organs. ii) Fine can continuum. addition most previous studies, suggest shedding underlying mechanism, this indicates cavitation another, potentially reversible, fuse’ mechanism. conclusion based on the very high vulnerability small diameter both Quercus and further this vulnerability drought-stressed roots. iii) study revealed two lines evidence existence asymmetry in below-ground competition: was over-proportionally reduced species-rich allospecific stand patches compared monospecific ones, growth rates and morphology depended competitor present but initial root size differences. iv) Tree may ranked according their ability. According to data experimentally altered neighbour-hoods, seems superior competitor belowground. marked outcome root competition only developed when summer was sufficiently high. Resource limitation, i.e. drought, to affect Quercus petraea similar manner consequence that species-specific differences less conspicuous more stressful environments. Therefore, overall importance direct biotic be reduced limited