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European Journal of Soil Biology
Volume 96, 2020, 103149

A long-term effect of Larix monocultures on soil physicochemical properties and microbes in northeast China

Jie Zhanga, Jianwei Zhangb, Lixue Yanga

Key Laboratory of Sustainable Forest Ecosystem Management-Ministry of Education, School of Forestry, Northeast Forestry University, Harbin, 150040, Heilongjiang, PR China.

Abstract

Forest monocultures are generally considered to alter the microbial community, reduce soil fertility, and presumably reduce forest productivity compared to mixed species in plantations or mixed species in natural stands. As the mechanisms of alteration of soils by monocultures have not been elucidated very well, we compared indicators of stand productivity and soils in three forest types all growing on the same soils that developed under the natural forests of the Maoershan Forest Farm in northeastern China. The three forest types were a planted monoculture of Larix plantation but where other species were allowed to ingrow (LP), a mixed species natural stand (NS), and a mixed species stand created by planting Larix seedlings into a natural stand (LP_NS). We measured the vegetation response as aboveground biomass (AGB), species richness and diversity, the soil response as soil physicochemical properties, and microbial community response as phospholipid fatty acids (PLFAs). The objectives were to determine (1) if the productivity of the Larix plantation was reduced relative to the natural stand, and if so, (2) which soil or microbial community factors were related to the declining productivity, and (3) how vegetation characteristics, soil physicochemical properties, and microbial community interacted. The three forest types appeared similar in aboveground biomass and litter biomass. As expected, 83% of 178.3 Mg ha-1 overstory AGB in LP was conifers and 87% of 134.7 Mg ha-1 AGB in NS was broadleaved species, and LP_NS with 176.9 Mg ha-1 had similar conifer AGB (53%) and broadleaved AGB (47%). Species richness for understory was greater in LP (N0 = 34, P < 0.05) than in NS (N0 = 22) and in LP_NS (N0 = 19); but species diversity was not different among the three forest types (2.1 = H= 2.7, P > 0.09). LP showed significant reductions (P < 0.006) in measures of soil fertility as lower soil N and P concentrations, lower soil pH, and higher soil bulk density than NS and LP_NS. Microbial PLFA did not differ among the three stands (P > 0.11) except for the ratios of G+/G-, sat/mono, and cy/prec PLFAs (P < 0.03). Our findings indicate that the plantation of Larix where ingrowth of other species occurred did not show declines in overstory productivity. However, AGB and litter biomass shifts from broadleaved species to conifers in LP relative to NS and LP_NS caused some soil changes that may relate to long-term productivity losses.

Keywords: Larix gmelinii plantation; Phospholipid fatty acids; Soil fertility; Soil microbial communities; Temperate deciduous secondary forests.

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