Root System Response To Water Supply And Its Foraging Strategy Of Typical Subtropical Tree Species

Root is the junction between the aboveground part of the plant and the soil and has plasticity in response to the change of environmental factors.At present,most studies on the response of roots to water and nutrients are limited to root growth,and there are relatively few studies on root topology and root formation foraging.In this paper,the responses of root growth and topology to water and nutrient of three typical subtropical tree species(Phyllostachys edulis,Pinus massoniana,Cunninghamia lanceolata)were studied,and the formation and foraging strategy of root system under different water and nutrient conditions were analyzed.Relationship between nutrient accumulation and distribution of photosynthetic products were studied.(1)Low concentration PEG(5%)drought stress inhibited the seed germination and radicle formation of moso bamboo,but significantly increased the final germination rate of moso bamboo and masson pine seeds and promoted the growth of moso bamboo.Low concentration PEG(5%)drought stress inhibited the germination of masson pine seeds and the growth of radicle during the whole germination stage,but increased the final germination rate of masson pine seeds.However,drought stress of high concentration PEG delayed seed germination of three tree species,decreased germination percentage and seedling growth during the whole germination period.Drought stress of different degrees inhibited seed germination and growth of Chinese fir.The drought critical value of Chinese fir Hypocotyl is lower than moso bamboo and masson pine.For the three species,seed germination was more sensitive to drought stress than the growth of radicle.(2)In order to study the adaptability strategies of three species roots under drought stress and the physiological mechanism of drought resistance,we compared the growth of the above-ground part,root architecture,and the concentration of non-structural carbohydrate in the roots of the seedlings under different levels of drought stress for different periods.The results showed that: the root and aboveground growth of the three species were significantlyinhibited by drought.In the aspect of root establishment strategy,three tree species showed various adaptive strategies.Moso bamboo responded to drought by reducing root diameter,fractal dimension,branching angle and increasing TI and NSC concentration in the root.Chinese fir responded to moderate drought by increasing diameter and root topological index,and to severe drought by increasing specific root length.During the whole drought period,masson pine was adapted to drought by reducing the specific root length and the length of fine roots and increasing the ratio of thick roots.(3)The foraging strategy of root in nutrient patch was studied by studying the growth,root distribution and establishment strategy of three species under the localized nutrient supply.The difference of tree species and nutrient significantly affected the response of roots to localized nutrient supply.The root plasticity of fibrous root species(moso bamboo,Chinese fir)is higher than that of tap root species(masson pine).Localized nitrogen supply and localized nitrogen plus phosphorus supply showed a significant positive effect on root proliferation of moso bamboo in nutrient-enriched layer.The distribution of Chinese fir roots in nutrient rich areas was significantly increased by localized nutrient supply,while masson pine was only sensitive to concentration of phosphorus.moso bamboo and Chinese fir increased root in nutrient rich areas,but also increased root in nutrient deficient layer,while masson pine showed root compensation.Moso bamboo reduced the building cost of roots in nutrient-enriched layer and nutrient deficient layers,while Chinese fir significantly increased the cost of root formation in nutrient enriched layer,thus increasing nutrient deficient layer and reducing internal competition of root system.The root formation strategy of masson pine is inflexible relatively.The promotion of NSC concentration in moso bamboo and Chinese fir root contributes greatly to the plasticity of the roots.(4)The foraging strategies of three tree species under different nutrient conditions were analyzed by comparing the configuration changes of roots under different fertilization intensities.N,P addition significantly promoted root growth and proliferation of three species,but had no significant effect on root growth at the early stage of experiment,and the effect of N addition on root architecture of moso bamboo was not significant.However,the fractaldimension and branching angle of Chinese fir root was significantly increased while root topological index were decreased.P addition decreased the branching angle of moso bamboo root and the root topological index of moso bamboo at the early stage of experiment.It also accelerated the root development of moso bamboo but did not affect the final branch complexity of moso bamboo.P addition decreased the branch angle and topological index of masson pine root,and promoted the development of masson pine root.