Effects of interactions of water and nutrients on root growth
Mostly, soil moisture influences nutrients availability and their transportation or uptake in root systems (Rouphael et al. 2012), i.e., in some cases, sufficient nutrients in soil does not guarantee to improve the plant growth during drought conditions (Rouphael et al. 2012). Therefore, to some extent, root growth can be influenced by the interactions between soil moisture and nutrients. As results showed in this study, SRL was influenced by the interactions of N × W and P × W. During the procedures of plants adapting environments, it is noteworthy that there would be trade-off between resource acquisition and resource conservation use strategies for plants to adapting soil heterogeneity (Fort et al. 2016). RTD, SRL and biomass are always seen as indicators assessing this trade – off. Under poor nutrients environments, plants will develop an acquisition resource use strategy by producing thin roots (with high SRL, low RTD and low biomass), which can elongate root systems for acquiring more nutrients and water (de Vries et al. 2016). And more, in this study, RTD and biomass both had negative correlation with SRL for S. breviflora . While under drought condition, there were higher SRL after 120 mg N / kg addition than that at 15 mg N / kg addition, which indicated that plants invest more thin roots, not for acquiring more nutrients or water, it seems to escape high level N and drought condition, which both inhibited the S. breviflora’s root growth. By contrast, in general, under nutrient – rich environments, plants would develop a conservation resource use strategy with producing coarse roots (with low SRL, high RTD and high biomass), which have higher ability in transporting nutrients and water (Hernández et al. 2010) and can store more resource with longer root spans than thin roots (Craine et al. 2001; de Vries et al. 2016; Fort et al. 2016). In this study, under low – level N addition, the root system ofS. breviflora’s would invest more coarser to store more organic matter for maximum longevity under drought environment, which may be related to 15mg/N addition being contribute to the root growth of S . breviflora . It indicated that high – level N addition caused S. breviflora to develop an acquisitive – resource – use strategy under drought condition, whereas developing a conservative – resource- use strategy under low – level N addition, one was for escaping and another for longevity. To some extent, higher SRL and lower biomass were found under 25 % FMC water addition (acquisition resource use strategy) than that under 75 % FMC water addition (conservation resource use strategy) under sufficient P condition, which indicated the former for acquiring more resource and later for storing more resource. This study was consistent with previous studies (Craine et al. 2001; de Vries et al. 2016; Fort et al. 2016).