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).