Liang Zong-suo

Community biomass of abandoned farmland and its effects on soil nutrition in the Loess hilly region of Northern Shaanxi, China

Abstract In order to have a basic knowledge of revegetation, one needs to deepen his understanding of the interactive effects of vegetation and soil. In this article, aboveground biomass, soil nutrients and moisture of 36 old-fields with different abandonment ages (from 2 to 45 years after abandonment), aboveground biomass of 4 typical old-fields, and growth characteristics of 7 predominant old-field species were measured. Changing pace, trend and relationship of community aboveground biomass and soil nutrition during the secondary succession were evaluated; effects of soil nutrition on community aboveground biomass were analyzed using multivariable analysis and pathway analysis, and effects of aboveground biomass on soil nutrition were further discussed. The results show that: (1) Soil nutrients, including organic matter, total nitrogen, total phosphorus, total potassium, nitrate nitrogen, ammonium nitrogen, active phosphorus and active potassium, have the same changing pace and trends as the aboveground biomass. In the process of secondary succession, both the soil nutrition and the community aboveground biomass decreased in the earlier abandonment stage of succession and then increased subsequently. (2) On the basis of the correlation of soil nutrients and abandonment ages, effects of vegetation on 0–20 cm organic matter, active phosphorus, 0–20 cm and 20–40 cm nitrate nitrogen nutrition are significant, while on the basis of the correlation of soil nutrition and aboveground biomass, no significant effects were observed. Hereinbefore, aboveground biomass accounts for only a part of vegetation-soil nutrition effects. The effects of biomass on organic matter, total nitrogen, total phosphorous, total potassium, nitrate nitrogen, active potassium and phosphorous are positive, whereas for ammonium nitrogen it is negative. (3) Abandonment ages, total nitrogen, total potassium, active potassium and soil moisture fluctuation have direct positive effects on the aboveground biomass of old-field communities; abandonment and soil moisture fluctuation have lager effects. Each ingredient of soil nutrition has relatively small effect, among which total nitrogen has larger effects than total and active potassium. The changes in aboveground biomass of old-field communities during succession are caused mainly by the changes in coverage and ecological characteristics of community species (the relatively larger direct effects of abandonment ages), and secondly by the soil moisture fluctuation (the relative smaller indirect effect of abandonment ages through soil moisture). (4) As a dependent variable, belowground biomass approaches power function of soil depth and declines in deeper layer. The root/shoot ratio of communities tends to increase in later succession stages, which also has an increasing tendency. These may influence the accumulation of biomass and decomposition of organic matter, and the vegetation-soil effects may be different.

Spatial heterogeneity of soil nutrients and aboveground biomass in abandoned old-fields of Loess Hilly region in Northern Shaanxi,China

Abstract Spatial heterogeneous characteristics of aboveground biomass and total soil nitrogen and phosphorus in old-field communities, Artemisia scoparia (early stage), Stipa bungeana (mid stage) and Lespedeza dahurica (later stage), in 0–20 cm and 20–40 cm depths with 3 different successional stages were studied using geostatistical methods. The correlations of aboveground biomass and total nitrogen and phosphorus at different scales were analyzed using partial Mantel correlation analyses on distance matrices. Moreover, the variations of aboveground biomass were partitioned into community space processes and environment components (including soil nitrogen and phosphorus). The results show that: 1) total phosphorus of the 3 communities has relatively larger spatial autocorrelation coefficients than total nitrogen. Total nitrogen of different layers also has different spatial heterogeneous extents. The variability of total nitrogen ranked as L. dahurica > S. bungeana > A. scoparia in 0–20 cm, and S. bungeana > L. dahurica > A. scoparia in 20–40 cm, so we infer that the variability of total nitrogen in the top layer increases as succession occurs, while in subsoil the variability of mid-succession stage is greater than that of earlier and later succession stages. The total phosphorus in both layers also has greater variability in mid-succession stage and smaller values in earlier and later succession stages. 2) Aboveground biomass of the 3 communities has different spatial autocorrelation coefficients, and S. bungeana has the smallest value. The variability ranked as A. scoparia > L. dahurica > S. bungeana. The partial Mantel correlogram of A. scoparia community shows significantly positive partial correlation at small scale (0.71 m) between aboveground biomass and total nitrogen, and relatively significantly negative correlation at small scale (0.71 m) between aboveground biomass and total phosphorus. For L. dahurica community, significantly positive correlation between aboveground biomass and total phosphorus occurred at 7.07–20.51 m scale, while at small scale (0.71 m) there also existed significantly positive correlation. No significant correlation was found for S. bungeana community with either total nitrogen or total phosphorus (only at small scale, the value was relatively great). 3) The environment, i.e., total nitrogen and phosphorus, explained about 19.59% of the spatial heterogeneity of aboveground L. dahurica biomass, 2.75% of A. scoparia and 1.95% of S. bungeana. The space process accounted for about 5.42% of the heterogeneity of A. scoparia, 1.79% of L. dahurica and 1.16% of S. bungeana.

Effects of soil drought on seedling growth and water metabolism of three common shrubs in Loess Plateau, Northwest China

The growth and water metabolism of three common shrubs on the Loess Plateau were studied under soil with different water contents. Results showed that water consumption of those species decreased with the increase in drought stress, and water consumptions of these shrubs were different: Forsythia suspensa was the greatest, and Syringa oblata was the lowest. The growth rate of new branches and leaf area of three species were the fastest under adequate soil water conditions, and were the lowest under severe drought. Under the same water conditions, the growth of F. suspensa was the fastest while that of S. oblata was the slowest. The water content, proline and chlorophyll content of different species changed with the increase in soil water stress. The leaf water content of Periploca sepium and F. suspensa was obviously higher than that of S. oblata, while the leaf proline content of F. suspensa and S. oblata was lower than that of P. sepium. The ratio leaf chlorophyll a: b of F. suspensa and S. oblata decreased with the decrease in soil water content. Although these three shrubs had different mechanisms in response to drought stress, they all had higher drought resistance and could adapt to the drought condition on the Loess Plateau. This paper provided some bases for choosing tree species on the Loess Plateau.