Phosphorus Resorption Efficiency Research Articles

Emergent macrophytes in phosphorus limited marshes: do phosphorus usage strategies change after nutrient addition?

Two strategies for phosphorus (P) economy in P-limiting environment are conservation of use and enhanced acquisition. Using two wetland macrophytes as an example, we show how these strategies change when the P-limitation is removed. Phosphorus resorption and activities of root phosphatases were evaluated over 4 years in Eleocharis cellulosa Torr. and Typha domingensis Pers. from nutrient addition experiment (P, N, N&P, control) established in 15 P limited marshes of Belize. We hypothesized that after P addition both species will increase tissue P content and decrease P resorption efficiency and root phosphatase activity. Initially high phosphorus resorption efficiency, PRE, significantly decreased in Eleocharis 2 years after the first nutrient addition, while no significant decrease was recorded for Typha. Even more dramatic was 5- to 6-fold increase in P in senescent tissues of Eleocharis as compared to less than 2-fold increase in Typha. Root phosphatase activity was high for both species from control plots. After P addition, Eleocharis showed 35% to 70% decrease in enzyme activity correlated to availability of inorganic P in sediments. Eleocharis and Typha employ the “conservation of use” strategy when growing in P limited oligotrophic marshes. In addition, Eleocharis is also using the “enhanced acquisition” strategy. These strategies change when the P limitation is removed but the response varies between the two species and thus changes in the proportion of these two species in a community may result in differences in ecosystem processes such as decomposition.

Influence of Site Fertility on N and P Resorption Efficiency in Native Tropical Tree Species Planted on Coal Mine Spoil

Nitrogen and Phosphorus resorption efficiency were studied along fertility gradient in eight native tropical tree species planted on coal mine spoil. The N and P resorption efficiencies decreased with increasing spoil fertility in all the tree species. The legumes and non-legumes potentially differed in terms of N and P resorption efficiently. The leguminous species had a higher efficiency for P resorption and a lower efficiency for N resorption than the non-leguminous species.

Contrasting nitrogen and phosphorus resorption efficiencies in trees and lianas from a tropical montane rain forest in Xishuangbanna, south-west China

Tropical montane rain forest is widely considered to be a highly threatened hotspot of global diversity (Brummitt & Nic Lughadha 2003), and one of the least understood humid tropical forest ecosystems in terms of nutrient cycling (Bruijnzeel & Proctor 1995). There is, therefore, an urgent need to improve our understanding of nutrient cycling processes in this ecosystem, including the absorption of nutrients (mainly N and P) from senescing leaves, which may be a key component of adaptive mechanisms that conserve limiting nutrients (Killingbeck 1996). Nutrients which are not resorbed, however, will be circulated through litterfall in the longer term (Aerts 1996). The degree of nutrient resorption affects litter quality, which consequently affects decomposition rates and soil nutrient availability (Aerts & Chapin 2000). The importance of resorption in nutrient conservation has led to general hypotheses that species adapted to nutrient-poor environments have high resorption efficiencies (Richardson et al. 2005), and that low leaf nutrient concentrations are associated with high resorption efficiencies within species (Aerts 1996, Kobe et al. 2005). Nutrient resorption has also been shown not to differ greatly between growth forms (e.g. shrubs, grasses, forbs and trees) (Aerts 1996). However, its relative importance among plant functional groups is still highly controversial (Richardson et al. 2005).

Nitrogen and phosphorus resorption efficiency and proficiency in six sub‐arctic bog species after 4 years of nitrogen fertilization

Summary 1 Plant growth at high-latitude sites is usually strongly nutrient-limited. The increased nutrient availability predicted in response to global warming may affect internal plant nutrient cycling, including nutrient resorption from senescing leaves. 2 The effect of increased N supply (10 g N m−2 year−1) on nitrogen and phosphorus resorption efficiency and proficiency in six sub-arctic bog species, belonging to four different growth-forms, was studied in northern Sweden. 3 We hypothesized that while increased N supply would not affect N or P resorption efficiency, it would lead to lower N resorption proficiency (higher N concentrations in leaf litter) and higher P resorption proficiency (lower P concentrations in leaf litter). We also investigated whether the basis on which resorption was expressed (leaf mass, leaf area or unit leaf) influenced the patterns observed. 4 Contrasting with our hypothesis, a general trend of decreased N resorption efficiency occurred in response to increased N supply, but the expected decrease in N resorption proficiency was seen in all species except Betula nana. 5 P resorption efficiency did not change in four species (B. nana, Empetrum hermaphroditum, Eriophorum vaginatum and Rubus chamaemorus) but it decreased in Andromeda polifolia, and increased in Vaccinium uliginosum. P resorption proficiency showed the expected increase in only two species (B. nana and V. uliginosum). 6 Apart from P resorption efficiency, the different calculation methods generally produced similar responses of resorption efficiency and proficiency to N supply. 7 Increased N supply at high-latitude sites clearly leads to more N being returned to the soil through leaf litter production. However, decomposition of such litter will probably become P-limited. 8 Considerable interspecific differences in nutrient resorption proficiency were found, indicating that long-term changes in vegetation composition need to be considered when evaluating plant-mediated effects on ecosystem nutrient cycling in response to increased nutrient supply.

Nitrogen vs. phosphorus limitation across an ecotonal gradient in a mangrove forest

Mangrove forests are characterized by distinctive tree-height gradientsthat reflect complex spatial, within-stand differences in environmentalfactors,including nutrient dynamics, salinity, and tidal inundation, across narrowgradients. To determine patterns of nutrient limitation and the effects ofnutrient availability on plant growth and within-stand nutrient dynamics, weused a factorial experiment with three nutrient treatment levels (control, N,P)and three zones along a tree-height gradient (fringe, transition, dwarf) onoffshore islands in Belize. Transects were laid out perpendicular to theshoreline across a mangrove forest from a fringe stand along the seaward edge,through a stand of intermediate height, into a dwarf stand in the interior ofthe island. At three sites, three trees were fertilized per zone for 2yr. Although there was spatial variability in response, growth byR. mangle was generally nitrogen (N) -limited in thefringe zone;phosphorus (P) -limited in the dwarf zone; and, N- and/or P-limited in thetransition zone. Phosphorus-resorption efficiency decreased in all three zones,and N-resorption efficiency increased in the dwarf zone in response to Penrichment. The addition of N had no effect on either P or N resorptionefficiencies. Belowground decomposition was increased by P enrichment in allzones, whereas N enrichment had no effect. This study demonstrated thatessential nutrients are not uniformly distributed within mangrove ecosystems;that soil fertility can switch from conditions of N to P limitation acrossnarrow ecotonal gradients; and, that not all ecological processes respondsimilarly to, or are limited by, the same nutrient.

Nutrient resorption in shrubs growing by design, and by default in Chihuahuan Desert arroyos

In the northern stretches of the Chihuahuan Desert, the margins of ephemeral stream channels called arroyos support a unique vegetation dominated by a guild of winter-deciduous shrubs. To explore the dynamics of nutrient conservation in this assemblage of arroyo shrubs, we measured nitrogen (N) and phosphorus (P) resorption efficiency and proficiency in six species of shrubs growing in arroyos in southern New Mexico. Collectively, these six species were no more efficient or proficient at resorbing N and P from senescing leaves than shrubs growing in other environments. Resorption efficiency averaged 53% and 50% for N and P, respectively, and resorption proficiency averaged 0.80% and 0.06% for N and P, respectively. However, resorption varied significantly between species specifically restricted in their distribution to riparian habitats (obligate riparian species), and those that were not. The two obligate riparian species combined (Brickellia laciniata, Chilopsis linearis) were significantly more efficient and proficient at resorbing N than the non-obligate riparian species combined (Fallugia paradoxa, Flourensia cernua, Prosopis glandulosa, Rhus microphylla). Additionally, both Brickellia and Chilopsis were individually significantly more proficient at resorbing N than any of the other four species. The dichotomy in resorption between obligate riparian species and those that were not may have been the result of the interplay between hydrology, geomorphology, and biology. Because arroyos move in space as the movement of water erodes banks and changes channel location, some plants are found along arroyos only because the arroyos have moved to them. These plants (plants growing by default) may be less well adapted to arroyo margins than obligate riparian species (plants growing by design). Significant differences in resorption between obligate and non-obligate riparian species suggested that evolutionary history and habitat specificity may be added to the list of factors known to influence resorption. Selected life history traits of the six species did not appear to be related to any measure of resorption, but leaf surface area, specific leaf mass, and nutrient concentrations in green leaves were all correlated with resorption efficiency or proficiency in one or more species. The only species capable of symbiotic N fixation, Prosopis glandulosa, retained at least 2.3 times more N in its senesced leaves than any other species. Patterns of resorption in arroyo shrubs strongly indicated that efficiency and proficiency are fundamentally different, complementary measures of resorption.

Effect of experimental phosphorus enrichment on oligotrophic tropical marshes in Belize, Central America

Sedges from genus Eleocharisdominate extensive wetlands in the sugar cane growing areas of the Caribbean. Correlative data suggest that macrophytes in these wetlands are phosphorus limited. To determine effects of increased P input that can be expected, e.g. from agricultural runoff, a common sugar cane fertilizer was applied to representative plots in four marl-based and four peat-based marshes. The plots were located in the proximity of patches of Typha domingensis, which has been reported to be able to outcompete Eleocharis under nutrient rich conditions. Responses to the fertilizer treatment were documented as changes in: Plant height, density, biomass, net primary production, nutrient resorption, decomposition, plant and soil nutrient concentrations, percent cover of cyanobacterial mats, and potential colonization by Typha. Additions of phosphorus significantly increased plant density and height and, consequently, the aboveground net primary production. Phosphorus resorption efficiency following senescence was independent of fertilizer addition in Eleocharis but decreased in Typha from the fertilized plots. Phosphorus resorption proficiency was lower in fertilized plots for both Typha and Eleocharis. Decomposition of litter and cellulose assays was significantly faster in fertilized plots. No spontaneous establishment of Typha occurred in the fertilized plots, but survival of transplanted Typha was higher in fertilized plots than in controls. Increased plant density in fertilized plots led to elimination of a key component of these ecosystems, the nitrogen fixing cyanobacterial mats.

Controls over Nutrient Resorption from Leaves of Evergreen Mediterranean Species

Nutrient resorption from senescent leaves, by minimizing nutrient losses, could be just as important as uptake in determining nutrient balance, especially in low—nutrient environments. To examine the relative importance of phenotypic and genotypic factors in controlling nutrient resorption, we sampled several meditterranean trees and shrubs growing in serpentine and nonserpentine soils in northern California. Plants growing in serpentine soils had smaller, thicker leaves than those growing in richer sites and had lower N and P concentrations and pools on a unit—area basis. Pools of nutrients resorbed and nutrients left in litter in rich—site leaves were larger than pools in poor—site leaves, but N resorption efficiency (percent of total leaf N resorbed) was higher in less fertile sites (65 vs. 46%). Differences in efficiency may be due to the ratio of soluble/nonsoluble proteins, which is higher at low—N sites. Trends for phosphorus resorption efficiency were not significant (47 vs. 46% in poor and rich sites, respectively). There were no significant differences among species adapted to poor vs. rich soils, nor between needle vs. broad—leaved species. We conclude that a high nutrient resorption efficiency is a phenotypic response to low—nutrient environments.

Larix laricina and Picea mariana: relationships among leaf life-span, foliar nutrient patterns, nutrient conservation, and growth efficiency

This study compared how two tree species with different leaf life-spans differ in their adaptations to low nutrient availability in a Wisconsin bog. Seasonal patterns of foliar nutrient concentration, nutrient resorption, leaching loss to simulated rainfall, and growth efficiency were determined for Larix laricina and Picea mariana during 1983 and 1984. Concentrations of foliar nitrogen and phosphorus in Larix leaves increased slightly during summer; this was followed by strong autumnal resorption. Calcium concentration of Larix leaves increased throughout the entire life-span of the leaves. Concentrations of nitrogen and phosphorus were highest in new (age-class 0) Picea leaves and declined with each successive leaf age-class, whereas calcium leaves increased in older leaf age-classes. Winter–spring resorption of nitrogen and phosphorus occurred from all age-classes of Picea leaves; this was followed by a summer increase in foliar nutrient concentrations. Resorption of nitrogen was greater in Larix than in Picea. There were no significant differences in phosphorus resorption or nutrient growth efficiencies between species. Foliar nutrient losses to leaching by artificial rainwater were less than 1% of the total foliar nutrient content. As there was no significant difference in the relative growth rates or growth efficiencies between the two species, the persistence of deciduous Larix in nutrient-poor bogs among species with longer leaf life-spans might be linked to its greater nitrogen conservation.