Fine Root Distribution Characteristics of Populus cathayana Plantations at Different Ages in Alpine Sandy Land

[Objectives]The paper was to study the fine root distribution characteristics of Populus cathayana plantations at different ages in alpine sandy land.[Methods]With 5,10,15,20,and 25 years old P.cathayana plantation in the eastern margin of Gonghe Basin,Qinghai Province as the research objects,fine roots were collected by root core drilling method,and the differences of fine root biomass,root length density,average diameter and root tip number at the soil depths of 0-20,20-40,40-60,60-80 and 80-100 cm were analyzed.[Results]The total biomass density of P.cathayana plantation was mainly distributed in the soil layer of 0-60 cm,accounting for 76%of the entire soil layer,and its value increased with the increase in forest age.With the increase in different forest ages,the root length density,average diameter and root tip number of living fine roots in the soil layer of 0-60 cm accounted for 74%-81%of the entire soil layer,and the proportions in the soil layers of 60-80 and 80-100 cm were 9%-11%.The biomass density,root length density,average diameter and root tip number of living and dead fine roots of P.cathayana plantation increased with the increase of forest age.The root length density,average diameter and root tip number of P.cathayana fine roots showed a linear function change trend with the growth of forest age,which could be described by the linear function equation y=ax+b(a>0).The analysis results showed that the root length density,average diameter and root tip number of P.cathayana were significantly correlated with the total biomass density of fine roots,and the root length density and average diameter had an extremely positive correlation with the total biomass density.[Conclusions]In the future,P.cathayana plantation should be properly tended to promote the development of fine roots and maximize its ecological benefits.

Sex-specific responses of tree-ring growth to climate in the dioecious tree Populus cathayana

Aims Radial growth in response to climate has been reported in many trees,but the sex-specific responses of tree-ring growth associated with altitude in dioecious trees are still poorly known.This study aims to examine whether(i)there are sex-related responses of tree-ring growth to climate in dioecious trees;(ii)these responses could be changed with altitude elevation.Methods The tree-ring width and basal area increment(BAI)were measured over the past 30 years(1982-2011),and the sexual differences in relationship between BAI and time span and correlations between ring width and climatic factors were investigated in Populus cathayana trees at two altitude sites(1,450 m and 1,750 m a.s.l.)in Xiaowutai Mountain,Hebei,north China.Important Findings The BAI was increased over the past 30 years.Trees at high-altitude sites had significantly lower mean ring width and mean BAI than those trees at low-altitude sites(P<0.001).In addition,sexual dif-ferences in tree-ring growth and its response to climate were more pronounced by altitude elevation.Male trees had a significantly larger mean ring width and mean BAI than did females at high-alti-tude sites,whereas no significant sexual differences in these traits were detected at low-altitude sites.Female trees were sensitive to previous October-November temperatures at high altitude but to current February and April precipitation at low altitude(P<0.05),whereas male trees were sensitive to current June temperature at high altitude but to January precipitation at low altitude(P<0.05).Our results indicated that the responses of tree-ring growth to cli-mate are sex dependent and can be changed with altitude elevation.

Sex-specifically responsive strategies to phosphorus availability combined with different soil nitrogen forms in dioecious Populus cathayana

Aims Phosphorus(P)availability and efficiency are especially important for plant growth and productivity.However,the sex-specific P acquisition and utilization strategies of dioecious plant species under different N forms are not clear.Methods This study investigated the responsive mechanisms of dioecious Populus cathayana females and males based on P uptake and allocation to soil P supply under N deficiency,nitrate(NO3−)and ammonium(NH4+)supply.Important Findings Females had a greater biomass,root length density(RLD),specific root length(SRL)and shoot P concentration than males under normal P availability with two N supplies.NH4+supply led to higher total root length,RLD and SRL but lower root tip number than NO3−supply under normal P supply.Under P deficiency,males showed a smaller root system but greater photosynthetic P availability and higher leaf P remobilization,exhibiting a better capacity to adaptation to P deficiency than females.Under P deficiency,NO3−supply increased leaf photosynthesis and P use efficiency(PUE)but reduced RLD and SRL in females while males had higher leaf P redistribution and photosynthetic PUE than NH4+supply.Females had a better potentiality to cope with P deficiency under NO3−supply than NH4+supply;the contrary was true for males.These results suggest that females may devote to increase in P uptake and shoot P allocation under normal P availability,especially under NO3−supply,while males adopt more efficient resource use and P remobilization to maximum their tolerance to P deficiency.

不同倍性青杨扦插苗对覆膜颜色的生长响应

以1年生二倍体(2×)、三倍体(3×)和四倍体(4×)青杨(Populus cathayana)扦插苗为试材,采用覆膜滴灌方式,设置3种不同颜色的地膜覆盖(红、黑、白),通过测定青杨的苗高地径、叶面积和根系形态,比较不同倍性青杨扦插苗对覆膜颜色的生长响应,以期为提高东北地区青杨苗木生长质量以及缩短青杨扦插苗的生长周期提供理论参考和技术支撑。结果表明:各种倍性苗木的苗高、地径和叶面积均在红色地膜覆盖下表现出一定的优势。综上所述,不同倍性苗木对膜色的生长响应基本一致,以红色地膜覆盖的表现最优。