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Abstract: Physiological and morphological plasticity of roots enhance plant nutrient uptake in spatiotemporally heterogeneous soil environments. We examined these two types of plasticity using three plant species (Solidago altissima (L.) [...]

Spatial variability of soil total nitrogen (N), available N (KCl extractable NH and NO), and spatial patterns of N mineralization and nitrification at a stand scale were characterized with geostatistical and univariate analysis. Two extensive soil spatial samplings were conducted in an evergreen broadleaf forest in Sichuan province, southwestern China in June and August 2000. In a study area of 90 × 105 m2, three soil samples were collected from each 5 × 5 m2 plot ( n = 378) in June and August, and were analyzed for total N and available N contents. Net N mineralization and nitrification were measured by in situ core incubation and the rates were estimated based on the difference of NH and NO contents between the two sampling dates. Total N, NH, and NO were all spatially structured with different semivariogram ranges (from high to low: NH, NO, and total N). The semivariograms of mineralization and nitrification were not as spatially structured as available N. NH was the dominant soil inorganic N form in the system. Both NH and NO affected spatial patterns of soil available N, but their relative importance switched in August, probably due to high nitrification as indicated by greatly increased soil NO content. High spatial auto-correlations (>0.7) were found between available N and NH4+, available N and NO on both sampling dates, as well as total N measurements between both sampling dates. Although significant, the spatial auto-correlation between NH and NO were generally low. Topography had significant but low correlations with mineralization ( r = −0.16) and nitrification ( r = −0.14), while soil moisture did not. The large nugget values of the calculated semivariograms and high-semivariance values, particularly for mineralization and nitrification, indicate that some fine scale (<5 m) variability may lie below the threshold for detection in this study. [ABSTRACT FROM AUTHOR]

Physiological and morphological plasticity of roots enhance plant nutrient uptake in spatiotemporally heterogeneous soil environments. We examined these two types of plasticity using three plant species (Solidago altissima (L.) Raf., Pinus taeda L., and Liquidambar styraciflua L.). We grew plants in pots (one plant per pot) with equal quantity of fertilizer applied either evenly over the pot surface (H) or on one-quarter of the pot surface (T). A high-concentration 15N-labeled ammonium nitrate solution was injected twice over 48 h before harvest at a random location in H pots, and in either unfertilized or fertilized portion of T pots. Physiological plasticity of N uptake was observed in S. altissima and L. styraciflua. The highest 15N uptake rate for L. styraciflua occurred in H pots (medium level), and that for S. altissima occurred in fertilized portions of T pots (rich level). When low-concentration 15N was added to S. altissima, no differences in uptake were noted among treatments, possibly because of interroot competition. In S. altissima and P. taeda, either morphological or physiological plasticity was strong. In L. styraciflua, both types of plasticity were strong. Total 15N uptake was enhanced when 15N was added to the fertilized patches. Physiological plasticity contributed >70% of enhanced 15N uptake in S. altissima and L. styraciflua. [ABSTRACT FROM AUTHOR]

Abstract: Eastern beech (Fagus orientalis Lipsky) is the major timber species growing in the Black Sea Region (BSR) forests of Turkey. Purple-flowered rhododendron (Rhododendron ponticum L.) is native to the region and currently dominates the understory of almost the entire eastern beech forest, reducing tree regeneration and growth. An aging beech overstory with little or no regeneration is the current state of most of the beech–rhododendron forests. We examined whether and how major environmental and disturbance factors have influenced the distribution and growth of rhododendron and beech in the region by determining the effects of canopy light, topography (aspect, elevation, slope), soil (moisture content, depth, texture, pH), and disturbance (anthropogenic and fire) on the establishment, abundance, and growth rate of rhododendron and beech in two rhododendron-invaded beech forests with different anthropogenic disturbance histories in the western BSR. We also studied the age and size structures of current beech stands and rhododendron to understand their origins and their future under varying levels of anthropogenic pressure. The two sites had different stem-size class distributions. A weak relationship was found between diameter at breast height and age for beech, whereas there was a strong correlation between groundline diameter and age for rhododendron. The rhododendron understory was established after the beech overstory. Charcoal-density analysis and beech stem ages suggested that fire has not been a major regenerative disturbance for these sites, at least in the past 150–200 years. Rhododendron reduced both beech regeneration and long-term growth. The rhododendron-population structure suggested continuing domination in the near future, with increasing density and proportion of small stems. Soil moisture was an important environmental factor affecting rhododendron and beech abundance and growth. Adequate soil aeration was critical for rhododendron. Use of foliar herbicides with burning during tree-regeneration efforts will probably provide greater success on rhododendron control. Establishing mixed beech-conifer stands might lower expansion of current and future rhododendron populations in the long term. [Copyright &y& Elsevier]

A study was conducted at the Savannah River Site in a 40-year-old slash pine (Pinus elliottii Engelm.) plantation in South Carolina to characterize the spatial patterns of soil, forest floor, and plant community variables and to investigate correlations among the variables. Spatial soil and litter samples were collected on five 0.25-ha plots.The spatial patterns of the variables were characterized by global variance, autocorrelation range, and patchiness. The cross-variable relationships were explored using Pearson's correlation tests to examine functional heterogeneity (i.e., to determine if structural heterogeneity reflected ecological processes). Variances of the variables calculated without regard to spatial position (i.e., global variance) were generally low. Average range of spatial autocorrelation was about 58 m for the forest floor variables, 11 m for soil variables, 11 m for basal area of large pines (>30 cm diameter at breast height), and less than 11 m for basal area of smaller pines or other woody species.Few strong spatial correlations among the forest floor and soil variables were observed. Spatial patterns of pines and hardwoods were weakly correlated with litter quality patterns and soil nitrogen. We conclude that the sample plots were generally homogeneous and that differences in soil resource levels were probably too small to influence spatial pattern of vegetation in this 40-year-old plantation. [ABSTRACT FROM AUTHOR]