| Korean Pine (Pinus koraiensis) is the dominant tree species in the climax community in northeast China, and is also one of the most common tree species planted in plantations. Therefore, it is very necessary to examine the factor that influencing the growth and carbon allocation of Korean pine plantations. Stand structure plays significant role in the growth and development of individual trees and biomass and productivity in stand level. However, previous studies mainly focused on the response of stand aboveground component(expecially in timber production) to silviculture practice and stand structure alternation, few studies have investigated the response of tree fine roots(typically less than2mm in diameter). Fine root, the primary absorbing organ of trees, plays a significant role in carbon allocation and nutrient cycling at stand level, via its production, growth, and death (turnover). So it is very important to study the relationship between stand structure and fine root production and biomass in order to understand the mechanism of forest productivity and work out appropriate silvicultureale policy. This study selected Korean pine plantations(43years old) with different stand structure: low density(represented by "low pine" below), high density (represented by"high pine" below), and stands with high proportions of hardwoods (represented by "hardwood" below). In September2011, fine root morphology (diameter, specific root length(SRL) and root tissue density), biomass, root length density and fine root vertical distribution pattern of different diameter classes(≤0.5mm,0.5-1.0mm,1.0-2.0mm,>2.0mm) were investigated using soil core method. In May2012, nitrogen were fertilized in low pine and high pine stands, and ingrowth cores were deployed to detect fine root production and its vertical distribution of different stands in the following growing season.1, the response of fine root diameter, SRL and tissue density to stand structure were different. Fine root in high pine stands were thicker in diameter, lower in SRL, but these difference were not statistically significant. Fine root diameter was thinner and SRL was higher in the top soil layer, but both were the opposite conditions in the bottom layer. Root tissue density was higher in hardwoods stands. According to two-way ANOVA, stand structure and soil layer had no obvious influence on fine root diameter and SRL, but root tissue density was significantly affected by both factors(P<0.05). The response of root tissue density to stand structure were mainly reflected in two root clusters:0.5-1.0mm and1.0-2.0mm, while the response to soil layer were reflected in root clusters≤0.5mm and0.5-1mm. In addition, the relationships between fine root diameter and SRL in all the soil layers could be fitted by negative exponential functions (P<0.01). 2^Stand structure had significant influence on fine root biomass and fine root length density. Fine root (≤2.0mm) biomass in low pine,high pine and hardwoods stands were300.9,456.2and221.8g·m-2respectively, root length density were2611.3,4914.5,1965.3m·m-2, respectively. Fine root biomass and fine root length density declined as soil depth increased in all stands, however, for thicker roots (>2.0mm), there were no consistent patterns in root biomass and soil depth in different stand types. Stand structure, diameter class and soil depth all had significant influence on root biomass and root length density, but only stand structure showed obviously effects for thinner absorbing root (≤0.5mm). High pine stands have significantly higher SRB and RLD than low pine and hardwoods. Stand structure also alterd the vertical distribution of SRB and RLD(P<0.05), for instance, the proportion of absorbing root biomass of Korean pine in the top layer were lower in hardwood stands than the other two types, while the proportion in the bottom layers were remarkable higher.3> Fine root production of Korean pine and hardwoods were different in the three stand types and their response to fertilization were various. In the fertilized treatment, fine root production of Korean pine and hardwoods were287.81and352.63g-m"2, while which in control treatment were126.22and141.39g·m-2respectively. Fine root production in low pine was significantly affected by fertilization, but there was no effect in high pine stands.Overall, stand structure showed influences on fine root morphology, biomass and root length density, thus, nutrient absorption of individual Korean pine and stand biomass and timber production could be altered. Nitrogen fertilization significantly decreased fine root production in Korean pine plantations, thus changed belowground carbon allocation and root litter input, while the fine root production of hardwoods may be stimulated. All these processes would exert important influences on nutrient cycling in forest ecosystem. Our results deepen our understanding of the relationship between stand structure and fine root biomass and production, providing necessary theoretical supports to scientific management of Korean pine plantations. |
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