The Role of Wood Ants (Formica rufa group) in Carbon and Nutrient Dynamics of a Boreal Norway Spruce Forest Ecosystem

Wood ants (Formica rufa group) are regarded as keystone species in boreal and mountain forests of Europe and Asia by their effect on ecosystem carbon (C) and nutrient pools and fluxes. To quantify the impact of their activity on boreal forest ecosystems, C, nitrogen (N), phosphorus (P), potassium (K) and calcium (Ca) pools and fluxes in wood ant nests (WAN), and soil were assessed along a 5-, 30-, 60-, and 100-year-old Norway spruce (Picea abies L. Karsten) dominated successional gradient in eastern Finland. Amounts of C and nutrients in WAN increased with stand age, but contained less than 1% of total C and nutrient pools in these stands. The CO₂-efflux from nests was also insignificant, as compared to CO₂-efflux from the forest floor. Annually, the amount of C brought by wood ants into their nests as honeydew, prey and nest-building materials ranged from 2.7 to 49.3 kg ha^?1 C, but this is only 0.1–0.7% of the combined net primary production of trees and understorey in boreal forests. The difference between wood ant nest C inputs and outputs was very small in the younger-aged stands, and increased in the older stands. Carbon accumulation rates in nests over a 100 year period are estimated to be less than 10 kg ha^?1 a^?1. In contrast to C, annual inputs of N, P, and K are larger compared to wood ant nest nutrient pool size, ranging from 3 to 6% of the annual tree stand and understorey uptake. This indicates a more rapid turnover and transport of N, P, and K out of WAN, and suggests that wood ants increase the cycling rate of these nutrients in boreal forests.     

Tree development in structural soil – an empirical below-ground in-situ study of urban trees in Copenhagen,Denmark

Aims

The purpose of this study is to evaluate root and stem growth, nutrient status and soil properties of a tree planting in structural soil.

Methods

Root and stem growth were measured at an 10-year-old urban planting of Tilia x europaea L. ‘Pallida’ established in structural soil on a paved square in Copenhagen, Denmark.Root abundance was quantified and soil profiles were established at three different distances from 10 trees (1.0, 1.9, and 2.9 m). Soil and leaf samples were analysed for nutrient concentrations.

Results

Abundant root presence was measured across the entire profile of structural soil (160?×?60 cm) at all distances, provided that structural soil layers were constructed correctly. Erroneously constructed structural soil layers however, resulted in impaired tree and root growth. Coarse root morphology was affected by the confined growing space in the voids of the stone matrix. The soil was relatively alkaline with an average pH (CaCl₂) of 7.3. Foliar analysis revealed deficiencies of K and Mn. These deficiencies might be due to a combined effect of high pH and low soil concentrations of these nutrients.

Conclusions

The study documents that correctly constructed structural soils allow and encourage root growth in load bearing layers.

     

The vertical distribution of N and K uptake in relation to root distribution and root uptake capacity in mature Quercus robur, Fagus sylvatica and Picea abies stands

We have measured the uptake capacity of nitrogen (N) and potassium (K) from different soil depths by injecting ¹⁵N and caesium (Cs; as an analogue to K) at 5 and 50 cm soil depth and analysing the recovery of these markers in foliage and buds. The study was performed in monocultures of 40-year-old pedunculate oak (Quercus robur), European beech (Fagus sylvatica) and Norway spruce (Picea abies (L.) Karst.) located at an experimental site in Palsgård, Denmark. The markers were injected as a solution through plastic tubes around 20 trees of each species at either 5 or 50 cm soil depth in June 2003. After 65 days foliage and buds were harvested and the concentrations of ¹⁵N and Cs analysed. The recovery of ¹⁵N in the foliage and buds tended to be higher from 5 than 50 cm soil depth in oak whereas they where similar in spruce and beech after compensation for differences in immobilization of ¹⁵N in the soil. In oak more Cs was recovered from 5 than from 50 cm soil depth whereas in beech and spruce no difference could be detected. Out of the three investigated tree species, oak was found to have the lowest capacity to take up Cs at 50 cm soil depth compared to 5 cm soil depth also after compensating for differences in discrimination against Cs by the roots. The uptake capacity from 50 cm soil depth compared with 5 cm was higher than expected from the root distribution except for K in oak, which can probably be explained by a considerable overlap of the uptake zones around the roots and mycorrhizal hyphae in the topsoil. The study also shows that fine roots at different soil depths with different physiological properties can influence the nutrient uptake of trees. Estimates of fine root distribution alone may thus not reflect the nutrient uptake capacity of trees with sufficient accuracy. Our study shows that deep-rooted trees such as oak may have lower nutrient uptake capacity at deeper soil layers than more shallow-rooted trees such as spruce, as we found no evidence that deep-rooted trees obtained proportionally more nutrients from deeper soil layers. This has implications for models of nutrient cycling in forest ecosystems that use the distribution of roots as the sole criterion for predicting uptake of nutrients from different soil depths.     

Nutrient transfer supports a beneficial relationship between the canopy ant,Azteca trigona,and its host tree

1. Energy fluxes between ants and plants have been a focal point for documenting mutualistic behaviour. Plants can provide resources to ants through the production of extrafloral nectaries. In exchange, ants can fertilise plants through their nutrient‐ and microbe‐rich refuse. 2. Here, we test a potential facultative mutualism between the carton‐nesting canopy ant, Azteca trigona, and their host trees. Through observational and experimental approaches, this study documents how nutrient transfer provides a basis for this beneficial ant–plant relationship. 3. In a greenhouse experiment, fertilisation with sterilised refuse (i.e. nutrients only) increased seedling growth three‐fold, while the refuse with its natural microbial community increased growth 11‐fold. 4. Total root density was doubled in refuse piles compared with the surrounding area in situ. On average, refuse provides host trees and the surrounding plant community with access to a > 800% increase in N, P and K relative to leaf litter. 5. Azteca trigona preferentially nests in trees with extrafloral nectaries and on large, longer‐lived tree species. 6. Given the nutrient‐poor nature of the Neotropics, host trees probably experience significant benefits from refuse fertilisation. Conversely, A. trigona benefit from long‐term stable structural support for nests and access to nutrient‐rich extrafloral nectaries. Without clear costs to either A. trigona or host trees, it is proposed that these positive interactions are preliminary evidence of a facultative mutualism.     

Growth and physiological responses of trembling aspen (Populus tremuloides), white spruce (Picea glauca) and tamarack (Larix laricina) seedlings to root zone pH

Background and aims

Soil pH is among the major environmental factors affecting plant growth. Although the optimum range of soil pH for growth and the tolerance of pH extremes widely vary among plant species, the pH tolerance mechanisms in plants are still poorly understood. In this study, possible mechanisms were examined to explain the differences in tolerance of boreal plants to root zone pH.

Methods

In the controlled-environment solution culture experiments, we compared growth, physiological parameters and tissue nutrient concentrations in aspen, white spruce and tamarack seedlings that were subjected to 8 weeks of root zone pH treatments ranging from 5.0 to 9.0.

Results

The pH treatments had little effect on dry weights and net photosynthesis in white spruce seedlings despite reductions in transpiration rates at higher pH levels. In aspen and tamarack, both the growth and physiological parameters significantly decreased at pH higher than 6.0. The chlorosis of young tissues in aspen and tamarack was associated with the reductions in foliar concentrations of several of the examined essential nutrients including Fe and Mn. Although the plants varied in their ability to deliver essential nutrients to growing leaves, there was no direct correlation between tissue nutrient concentrations, chlorophyll concentrations and plant growth. The results also demonstrated strong inhibition of transpiration rates by high pH.

Conclusions

The results suggest that high root zone pH can upset water balance in pH sensitive species including aspen. Although the uptake and assimilation of essential elements such as Fe and Mn contribute to plant tolerance of high soil pH, we did not observe a direct relationship between growth and foliar nutrient concentrations to account for the observed differences in growth.     

Leaf‐cutting ants as ecosystem engineers: topsoil and litter perturbations around Atta cephalotes nests reduce nutrient availability

相似文献   

Plant-soil feedback in spruce (Picea abies) and mixed spruce-beech (Fagus sylvatica) stands as indicated by dendrochemistry

Ten pairs of secondary pure spruce (Picea abies) and adjacent mixed spruce-beech (Fagus sylvatica) stands on comparable sites were selected on two different bedrocks for soil formation (Flysch: nutrient rich and high soil pH; Molasse: poor nutrient supply and acidic) to study how an admixture of beech to spruce stands affects nutrient cycling and consequently soil chemistry. Soil analyses indicated accumulation of Ca under the mixed stands while the top soil under pure spruce was acidified. It was hypothesized that changes of soil chemical properties due to species composition over the last six decades are reflected in the stem wood of spruce. Three healthy dominant spruce trees per plot were selected for coring. Cores were crossdated and half-decadal samples were analyzed for Ca, Mg, Mn and Al. Calcium and Mg concentrations in stem wood of spruce were significantly higher for the pure spruce than for the mixed stands in spite of lower Ca and Mg stores in the soil. We assume that acidification caused by pure spruce mobilized these cations temporarily, increasing soil solution contents and consequently stem wood concentrations. It was possible to reconstruct soil pH from the element ratios Ca/Al (pure stands) and Ca/Mg (mixed stands), since these ratios in the stem wood of the last half-decade did correlate with soil pH for selected soil depths. Reconstructed soil pH showed a decline over the last 60 years under both species compositions due to accumulation of base cations in the increasing biomass. Comparisons of reconstructed soil pH in 0–5 and 10–20 cm soil depth indicated more pronounced top soil acidification (lower soil pH in 0–5 cm) by spruce on the nutrient rich soil (Flysch) than on the acidic soil (Molasse). However, admixture of beech caused higher pH values in 0–5 cm than in 10–20 cm soil depth on Flysch due to the observed Ca-pump effect of beech (uptake of Ca from deeper soil horizons).     

The relation among soil microorganism, enzyme activity and soil nutrients under subalpine coniferous forest in Western Sichuan

Soil microorganism and enzymes are important parts of forest ecosystem and sensitive to environmental changes. They have many critical functions in energy conversion and material cycle of forest soil. However, there are few studies about soil biological properties under subalpine coniferous forest, in particular, a serial of spruce plantation chronosequences following clear-cutting of natural coniferous forest in western Sichuan. We measured the quantity of soil microorganism (including bacteria, fungi and actinomyces), enzyme activity and soil nutrients under spruce plantation chronosequences in western Sichuan to investigate soil biological properties and their relationship with soil nutrients. The results showed that soil microorganism, enzyme activity and soil nutrients of the mature spruce plantation were significantly lower than those of the young spruce plantation and secondary broad-leaved forest. Soil fertility degraded greatly with the increasing of spruce plantation age and was mainly affected by forest micro-environment. There were significant correlation between the amounts of soil microorganisms, soil enzyme activities and nutrients (e.g. soil organic matter, total N, total P, alkali-hydrolyzable N and available K). Therefore soil biological indices can be used to evaluate soil fertility. In order to accelerate the course of restoration and rehabilitation of degraded pure plantation, the strategy and measures were put forward, including application of thinning rationally for existing dense plantations and establishment of mixture forest of coniferous and broad-leaved trees for new afforestations, which would create good forest micro-environment for plant growth.     

The relation among soil microorganism, enzyme activity and soil nutrients under subalpine coniferous forest in Western Sichuan

Soil microorganism and enzymes are important parts of forest ecosystem and sensitive to environmental changes. They have many critical functions in energy conversion and material cycle of forest soil. However, there are few studies about soil biological properties under subalpine coniferous forest, in particular, a serial of spruce plantation chronosequences following clear-cutting of natural coniferous forest in western Sichuan. We measured the quantity of soil microorganism (including bacteria, fungi and actinomyces), enzyme activity and soil nutrients under spruce plantation chronosequences in western Sichuan to investigate soil biological properties and their relationship with soil nutrients. The results showed that soil microorganism, enzyme activity and soil nutrients of the mature spruce plantation were significantly lower than those of the young spruce plantation and secondary broad-leaved forest. Soil fertility degraded greatly with the increasing of spruce plantation age and was mainly affected by forest micro-environment. There were significant correlation between the amounts of soil microorganisms, soil enzyme activities and nutrients (e.g. soil organic matter, total N, total P, alkali-hydrolyzable N and available K). Therefore soil biological indices can be used to evaluate soil fertility. In order to accelerate the course of restoration and rehabilitation of degraded pure plantation, the strategy and measures were put forward, including application of thinning rationally for existing dense plantations and establishment of mixture forest of coniferous and broad-leaved trees for new afforestations, which would create good forest micro-environment for plant growth.     

Alternate Bearing Affects Nitrogen, Phosphorus, Potassium and Starch Storage Pools in Mature Pistachio Trees

The relationship between crop load and the functional storageof selected macronutrients and starch was assessed to developnutrient budgets and best management fertilization practicesin orchards. Functional storage represents the amount of nutrientsand starch redistributed from perennial tree parts in supportof the spring growth flush. Functional storage was influencedby:(a)nutrient and starch accumulation prior to dormancy; and(b)nutrientand starch demand by vegetative and reproductive organs in spring.Lightly cropping (off-year) trees stored 7, 14 and 2 times asmuch N, P and K, respectively, as heavily cropping (on-year)trees. Similar to many biennial plant species, nutrients thataccumulated during the vegetative phase in off-year trees wereused to support reproductive growth during the subsequent on-year.Soil nutrient uptake contributed more to storage pools thanleaf nutrient resorption in off-year-trees, while the reversewas true in on-year trees. Net nutrient resorption from senescingleaves accounted for all of the N and P and a third of the Kstored in on-year trees. Only between 20–33% of the N,P and K stored in perennial tissues of off-year trees couldbe attributed to leaf nutrient resorption. This is the firststudy to determine the amounts of nutrients stored in the perennialparts of mature, field-grown trees and the relative contributionsof leaf nutrient resorption and soil nutrient uptake to functionalstorage in trees.Copyright 1998 Annals of Botany Company Pistacia vera, nutrient storage, biennial bearing, crop load, leaf nutrient resorption, source-sink relationships.     

Nutrient Cycling and Nutrient Use Efficiency in Short Rotation,High Density Central Himalayan Tarai Poplar Plantations

This paper deals with the pattern of nutrient cycling and nutrient use efficiency in four (1–4 years old) poplar (Populus deltoidesMarsh) plantations previously investigated for dry matter dynamics. The present plantations were planted at 3×5 m spacing after clear felling of natural sal (Shorea robustaDipterocarpaceae) mixed broad-leaved forests in central Himalayan Tarai. The nutrient concentrations (N, P and K) in different layers of vegetation were in the order: tree>shrub>herb; whereas the standing state of nutrients were in the order: tree>herb>shrub. Soil, litter and vegetation, respectively accounted for 81–96, 2–4 and 2–15% of the total nutrients in the system. Considerable reductions (trees, 50–68; shrubs, 35–40; and herbs 18–26%) in the concentration of nutrients in leaves occurred during senescence. The uptake of nutrients by the vegetation, and also by the different components, with and without adjustment for internal recycling, was calculated separately. Annual transfer of litter nutrients to the soil by vegetation was 91–148 N, 8–15 P and 70–99 K kg ha⁻¹yr⁻¹. The turnover rate for different nutrients ranged between 0.83 and 0.92 yr⁻¹. The nutrient use efficiency of poplar plantations ranged from 151 to 174 kg ha⁻¹yr⁻¹for N, 1338 to 1566 kg ha⁻¹yr⁻¹for P, and 313 to 318 kg ha⁻¹yr⁻¹for K. Compared with low density eucalypt and older poplar stands, there was a higher proportion of nutrient retranslocation in present poplars, largely because of higher tissue nutrient concentrations. This indicates lower nutrient use efficiency as compared to eucalypt plantations. Compartment models for nutrient dynamics have been developed to represent the distribution of nutrient pools and net annual fluxes within the system.     

Effect of annual variation in soil pH on available soil nutrients in pear orchards

Soil pH is an important factor affecting the availability of soil nutrients that impact plant growth. Given the susceptibility of soil pH to excessive fertilization and the widespread use of manures, it is essential to examine the influence of soil pH on the distribution and availability of soil nutrients. We sampled and analyzed brown soils from pear orchards in thirteen towns in Wendeng county. Samples were obtained from areas along or between rows of trees at specified distances and depths. The results showed that the soil pH fluctuated from 4.06 to 6.59 in October 2008 and from 4.24 to 7.57 in April 2009. The quantity of soil samples with pH below 5.50 increased by 34.6%. Analysis of the soil pH for samples obtained along the rows of trees showed that the pH decreased as the depth increased (except for the range 5.5 to 6.0); soil pH in the samples obtained between the rows of trees demonstrated different trends. The average organic matter (O.M.) content as well as the N (NH₄⁺) and available P, K, Cu, Zn, Fe, and Mn contents in the samples collected in October 2008 were higher than those observed in April 2009. Conversely, the values for other available nutrients were lower than those in the samples collected in April 2009. The available nutrients and organic matter (O.M.) content in different pH ranges varied. The soil pH was significantly or very significantly correlated with N (NH₄⁺ and NO₃^-), available K, Cu, Fe, and exchangeable Ca for the October 2008 samples, while a significant or very significant correlation existed between N (NH₄⁺), available P, Zn, exchangeable Ca, and exchangeable Mg for the April 2009 samples. The correlations between soil pH and the amounts of available nutrients and organic matter (O.M.) along the rows of trees in September 2009 were nearly consistent with those between the rows.     

Effect of annual variation in soil pH on available soil nutrients in pear orchards

Soil pH is an important factor affecting the availability of soil nutrients that impact plant growth. Given the susceptibility of soil pH to excessive fertilization and the widespread use of manures, it is essential to examine the influence of soil pH on the distribution and availability of soil nutrients. We sampled and analyzed brown soils from pear orchards in thirteen towns in Wendeng county. Samples were obtained from areas along or between rows of trees at specified distances and depths. The results showed that the soil pH fluctuated from 4.06 to 6.59 in October 2008 and from 4.24 to 7.57 in April 2009. The quantity of soil samples with pH below 5.50 increased by 34.6%. Analysis of the soil pH for samples obtained along the rows of trees showed that the pH decreased as the depth increased (except for the range 5.5 to 6.0); soil pH in the samples obtained between the rows of trees demonstrated different trends. The average organic matter (O.M.) content as well as the N (NH₄⁺) and available P, K, Cu, Zn, Fe, and Mn contents in the samples collected in October 2008 were higher than those observed in April 2009. Conversely, the values for other available nutrients were lower than those in the samples collected in April 2009. The available nutrients and organic matter (O.M.) content in different pH ranges varied. The soil pH was significantly or very significantly correlated with N (NH₄⁺ and NO₃^-), available K, Cu, Fe, and exchangeable Ca for the October 2008 samples, while a significant or very significant correlation existed between N (NH₄⁺), available P, Zn, exchangeable Ca, and exchangeable Mg for the April 2009 samples. The correlations between soil pH and the amounts of available nutrients and organic matter (O.M.) along the rows of trees in September 2009 were nearly consistent with those between the rows.     

喀斯特木论自然保护区土壤养分的空间变异特征

基于网格(20m×20m)采样法采集土壤样品,利用经典统计学和地统计方法分析了典型喀斯特峰丛洼地(200m×100m)土壤养分的空间变异特征.结果表明:研究区土壤pH值表现为弱变异,其他各养分指标均为中等程度变异,大小顺序为速效磷(AP)速效钾(AK)碱解氮(AN)土壤有机质(SOM)全钾(TK)全磷(TP)全氮(TN);pH半变异函数的最佳拟合模型为球状模型,TK和AK的最佳拟合模型为指数模型,其他养分指标的最佳拟合模型均为高斯模型;pH、AK的变异尺度(变程)较小,分别为58.1和41.1m,SOM、TN、TP、AN、AP的变异尺度相近,在100～150m,TK的变异尺度最大(463.5m);除研究区土壤TK、TN表现为中等的空间自相关性外,其他土壤养分指标均表现为强烈的空间自相关性.pH、AK呈零星斑块状分布,表现为高异质性;SOM、TP、TK的变化趋势较平缓,呈中间高、两边低的分布格局;AN、AP的空间分布具有显著的相似性,均随坡度的增加而呈片状上升趋势;TN的分布较特殊,呈中间低、两边高的趋势.植被、地形和高异质性的微生境是造成喀斯特木论自然保护区土壤养分格局差异的主要因素.     

Wood ants and a geometrid defoliator of birch: predation outweighs beneficial effects through the host plant

Soil amelioration by a wood-ant species and its consequences for the larval performance of autumnal moths feeding on mountain birch were studied at various distances from the nest mound. Soil nitrate and ammonium nitrogen did not show any clear relationship with distance. However, trees growing in the mound had over 20% more foliar nitrogen than more distant trees. When moth larvae were experimentally protected from predation, their survival rate and final weight tended to decrease with increasing distance. In a laboratory experiment with detached leaves, the relative growth rate of larvae was roughly 30% higher on leaves from trees located on the mound. Differences in larval performance refute the Plant Stress Hypothesis proposed by T.C.R. White and support P.W. Price's Plant Vigor Hypothesis. Predation by ants was examined along the same gradient in trees with and without a glue band that excluded ants from the canopy. Reduction in the daily survival rate of larvae attributable to ant predation was about 35% in trees growing in the mound and around 5% at a distance of 20 m. Other things being equal, about 25 times more larvae entering the penultimate instar would achieve the pupal stage outside the wood-ant territory than in the vicinity of the mound. While both the fertilizing and predatory influence of wood ants is clear, the domain of predation is much larger than the area where trees and their herbivores can exploit enhanced nutrient levels in and around ant mounds. The existence of undamaged green islands around ant mounds in otherwise totally defoliated mountain-birch forests cannot be explained by soil amelioration by wood ants but rather by their predatory activity. Received: 21 November 1996 / Accepted: 8 September 1997     

Site factors,foliar nutrient levels and growth of Cordia alliodora plantations in the humid lowlands of Northern Costa Rica

Within the perhumid, Atlantic lowlands of northern Costa Rica, Cordia alliodora plantations were studied in order to explain the observed pattern of growth irregularities. The soils, that were partly used as pastures over long periods, could be classified roughly into two units: (i) red, deeply weathered, slightly acidic soils from Mg-enriched parent material and (ii) brown, strongly acidic soils with high saturation of exchangeable Al (up to 80%).Leaf analysis revealed that Cordia is a highly demanding species in respect to macronutrients. Poorly growing trees in slope position suffered from an insufficient supply of N and P. K/Mg ratios of chlorotic leaves are very low. Soil analysis showed that nutrient deficiencies were related to (i) insufficient soil nutrient reserves of the poor, tropical soils or (ii) to an inhibition of nutrient uptake by soil physical or chemical factors.All sites are characterized by very low K reserves and losses of nutrients that are organically bound (N, P) caused by erosion. In the Mg-rich red soils, low amounts of K lead to K/Mg imbalances. Soil compaction caused by cattle grazing occurs on both soil units. In negatively influences the root development of Cordia, and hence nutrient uptake. In the brown soils, high amounts of exchangeable Al hinder a sufficient supply of nutrients (e.g.P) to the assimilation organs.     

Leaf‐cutting ants,seasonal burning and nutrient distribution in Cerrado vegetation

Abstract Fire and herbivory are known to modify plant community structure. Many studies have suggested that fire ashes may increase soil nutrients in dystrophic soils. Herbivores may also change plant community structure through direct effects of herbivory and affecting nutrient cycling. Leaf‐cutting ants were traditionally viewed as herbivores, although their role may be more complex, because their nests affect both chemical and physical soil properties, thus affecting plants indirectly. We investigated the effects of frequent burning and of leaf‐cutting ants on the nutrient status of an herbaceous and a shrub species occurring in the Brazilian Cerrado, a habitat that is characterized by natural burnings. The proximity of ant nests resulted in an increase of nutrients in the leaves of both vegetation strata, whereas burning sometimes resulted in a decrease of nutrients. Our results do not lead to a possible positive effect of fire on plant nutrient content. On the other hand, ant nests may represent an important source of nutrients for plants on the nutrient‐depleted Cerrado soils and may accelerate vegetation recovery after burning.     

Green Islands — nutrition not predation —an alternative hypothesis

Summary Mountain birch trees are said to survive as green islands around nests of red ants in Finnish Lapland because the ants kill larvae which would defoliate trees during outbreaks of the moth O. autumnata. An alternative hypothesis says that because the ants will concentrate soil nutrients (and possibly ameliorate soil moisture and temperature) in and around their nests, they provide a more favourable site for trees growing nearby. These trees are therefore less stressed and a poorer source of food for defoliators at times of outbreaks. Few if any young O. autumnata larvae survive on the trees which then survive in green islands around ant nests.     

红壤旱坡地农田生态系统养分循环和平衡

通过田间定位试验从生态系统的角度比较研究了中亚热带红壤低丘岗地几种主要旱坡地农田生态系统的水土流失、养分循环和平衡特征、土壤养分消长动态及空间分异,结果表明：水土流失是红壤旱坡地生态系统养分损失的重要途径之一,固体径流具有养分富集现象,速效养分损失以地表径流为主,水土流失养分损失量大小顺序为：有机碳＞全钾＞速效钾＞全氮＞全磷＞水解氮＞速效磷;免耕覆盖和垄作能显著减少水土流失及养分损失量;红壤旱地淋溶也是养分,尤其是氮素损失的重要途径;在养分平衡有盈余状况下,土壤养分水平是可以逐步提高的,其中,土壤速效磷、速效钾提高的速度较快,土壤全氮、有机质和全磷也有所提高,但仍处于较低水平;复合农林系统中,土壤养分存在明显的空间分异,农作物区域由于养分投入较高,土壤养分水平明显高于林木区域。     

Nutrient dynamics in crown tissues of cork-oak (Quercus suber L.)

The seasonal fluctuation of N, P, K, Ca and Mg in leaves, young stems and fruits of young and matureQuercus suber trees growing at the same site was studied. Nutrient dynamics within the tree appeared to be linked to phenological events. Leaves maximized their nutrient contents throughout summer whereas stems maintained rather constant values during most of the year. Before the spring growth flush they apparently acted as temporary reservoirs for some nutrients, translocated from leaves or other organs, so that such nutrients would be easily invested in the new tissues. A significant investment was made in sink organs like flowers and fruits. The tree probably relies not only on leaves but also on other nutrient reservoirs like older branches and roots for an adequate supply to those sinks and to the spring growth. The importance of the sampling dates and the basis of expression used for nutrient concentrations has also been emphasized. Nutrient contents and seasonal trends of the studied trees were similar to those of other evergreen oaks, although somewhat higher values for N, K, and Mg were found. Moreover, soil nutrient contents in the studied montado were much lower than in other Iberic oak stands. However the nutrient status and requirements of cork-oak suggest high (or at least adequate) nutrient availability to the trees. The mechanisms by which this could be achieved are discussed.