Kanehiro Kitayama

Changes in Soil Phosphorus Fractions and Ecosystem Dynamics across a Long Chronosequence in Hawaii

We tested the Walker and Syers (1976) conceptual model of soil development and its ecological implications by analyzing changes in soil P, vegetation, and other ecosystem properties on a soil chronosequence with six sites ranging in age from 300 yr to 4.1 x 10 6 yr. Climate, dominant vegetation, slope, and parent material of all of the sites were similar. As fractions of total P, the various pools of soil phosphorus behaved very much as predicted by Walker and Syers. HCl-extractable P (presumably primary mineral phosphates) comprised 82% of total P at the 300-yr-old site, and then decreased to 1% at the 20,000-yr-old site. Organic phosphorus increased from the youngest site to a maximum at the 150000 yr site, and then declined to the 4.1 x 10 6 yr site. Occluded (residual) P increased steadily with soil age. In contrast to the Walker and Syers model, we found the highest total P at the 150000-yr-old site, rather than at the onset of soil development, and we found that the non-occluded, inorganic P fraction persisted through to the oldest chronosequence site. Total soil N and C increased substantially from early to middle soil development in parallel with organic P, and then declined through to the oldest site. Readily available soil P, NH 4 + , and NO 3 - were measured using anion and cation exchange resin bags. P availability increased and decreased unimodally across the chronosequence. NH 4 + and NO 3 - pools increased through early soil development, but did not systematically decline late in soil development. In situ decomposition rates of Metrosideros polymorpha litter were highest at two intermediate-aged sites with high soil fertility (20000 yr and 150000 yr), and lowest at the less-fertile beginning (300 yr) and endpoint (4.1 x 10 6 yr) of the chronosequence. M. polymorpha leaves collected from these same four sites, and decomposed in a common site, suggested that leaves from intermediate-aged sites were inherently more decomposable than those from the youngest and oldest sites. Both litter tissue quality and the soil environment appeared to influence rates of decomposition directly. The highest mean soil N 2 O emissions (809 μg.m -2 .d -1 ) were measured at the 20 000-yr-old site, which also had the highest soil nitrogen fertility status. Plant communities at all six chronosequence sites were dominated primarily by M. polymorpha, and to a lesser extent by several other genera of trees and shrubs. There were, however, differences in overall vegetation community composition among the sites. Using a detrended correspondence analysis (DECORANA), we found that a high proportion of species variance among the sites (eigenvalue = 0.71) can be explained by site age and thus soil developmental stage. Overall, long-term soil development across the chronosequence largely coincides with the conceptual model of Walker and Syers (1976). How P is distributed among different organic and inorganic fractions at a given stage of soil development provides a useful context for evaluating contemporary cycling of P and other nutrients, and for determining how changes in P availability might affect diverse ecosystem processes.

An altitudinal transect study of the vegetation on Mount Kinabalu, Borneo

A quantitative transect analysis of altitudinal sequences of forest canopy species from 600 to 3400 m asl on Mt. Kinabalu (4101 m), Borneo, resulted in four discrete altitudinal vegetation zones. These were made up of mutually exclusive species groups for lowland (<1200 m asl), lower montane (1200 to 2000–2350 m asl), upper montane (2000–2350 to 2800 m asl), and subalpine (2800 to the forest line, 3400 m asl) zones. Zonal soil types were correlated with the vegetation zones. In upslope sequence, these were: lowland Oxisols, montane Histosol/Spodosol complex, and subalpine Inceptisols. The highest contents of organic carbon, extractable phosphorus, and exchangeable magnesium and potassium were recorded in the lower and upper montane zones. The upper boundaries of the lowland, upper montane and subalpine zones coincided with thermal thresholds of latitudinal bioclimatic zones: 18°C TMIN (Köppens tropical), WI 85 (Kiras warm temperate), and WI 45 (Kiras cool temperate), respectively. The upper limit of the lower montane zone was correlated with an abrupt increase of water surplus estimated from the annual rainfall minus annual potential evaporation. These climatic characteristics appear to define ecological altitudinal turnover points, so called ‘critical altitudes’, where groups of associated species are displaced by other groups.

Temperature Influences Carbon Accumulation in Moist Tropical Forests

Evergreen broad-leaved tropical forests can have high rates of productivity and large accumulations of carbon in plant biomass and soils. They can therefore play an important role in the global carbon cycle, influencing atmospheric CO2 concentrations if climate warms. We applied meta-analyses to published data to evaluate the apparent effects of temperature on carbon fluxes and storages in mature, moist tropical evergreen forest ecosystems. Among forests, litter production, tree growth, and belowground carbon allocation all increased significantly with site mean annual temperature (MAT); total net primary productivity (NPP) increased by an estimated 0.2-0.7 Mg C x ha(-1) x yr(-1) x degrees C(-1). Temperature had no discernible effect on the turnover rate of aboveground forest biomass, which averaged 0.014 yr(-1) among sites. Consistent with these findings, forest biomass increased with site MAT at a rate of 5-13 Mg C x ha(-1) x degrees C(-1). Despite greater productivity in warmer forests, soil organic matter accumulations decreased with site MAT, with a slope of -8 Mg C x ha(-1) x degrees C(-1), indicating that decomposition rates of soil organic matter increased with MAT faster than did rates of NPP. Turnover rates of surface litter also increased with temperature among forests. We found no detectable effect of temperature on total carbon storage among moist-tropical evergreen forests, but rather a shift in ecosystem structure, from low-biomass forests with relatively large accumulations of detritus in cooler sites, to large-biomass forests with relatively smaller detrital stocks in warmer locations. These results imply that, in a warmer climate, conservation of forest biomass will be critical to the maintenance of carbon stocks in moist tropical forests.

Foliar Nutrients During Long‐Term Soil Development in Hawaiian Montane Rain Forest

We determined the consequences of systematic changes in nutrient availability during long-term soil development by measuring foliar nutrient concentrations. Sun leaves of the dominant tree Metrosideros polymorpha and of eight other species were sampled in Hawaiian rain forests developed on substrates that were 0.3 x 10 3 , 2.1 x 10 3 , 5 x 10 3 , 20 x 10 3 , 150 x 10 3 , 1400 x 10 3 , and 4100 x 10 3 yr old. Elevation, annual precipitation, parent material, and dominant species were nearly constant along this gradient. Foliar N and P concentrations in Metrosideros were lowest in the youngest site (0.72% and 0.052% for N and P, respectively), increased to a maximum on 20 X 10 3 and 150 x 10 3 -yr-old substrates (1.45% and 0.108%), and then declined close to the initial concentrations in the oldest site (0.86% and 0.061%); N:P ratios in foliage varied relatively little across the sites. Most other species followed a similar pattern of variation. On a per unit leaf area basis, foliar N and P contents in Metrosideros also peaked on intermediate-aged substrates. Foliar nutrient concentrations in Metrosideros sun leaves were determined across a parallel but wetter substrate age gradient. The pattern of variation was similar on both gradients, but the magnitude of variation was smaller on the wetter sequence of sites. Overall, the pattern of variation in foliar nutrients with substrate age is consistent with conceptual models for the dynamics of soil nutrient availability during long-term soil development, and with measurements of soil properties along this sequence.

Effects of topography on tropical lower montane forests under different geological conditions on Mount Kinabalu, Borneo

Species composition and forest structure change with topography.However, mechanisms for topographical vegetation changes are still not wellunderstood, because a topographical gradient is a complex environmentalgradientinclusive of many factors. The foot of Mt. Kinabalu is covered with three typesof geological substrates, i.e. Quaternary and Tertiary sedimentary rocks andultrabasic (serpentine) rock. Quaternary and Tertiary sedimentaryrocks are different in site age, but controlled in primary minerals. Tertiarysedimentary and ultrabasic rocks are contrasting in primary minerals, but arecomparable in age. This setting provides an opportunity to examine thevegetation differentiation along topographical gradients that are contrastinginmajor-nutrient supply due to the difference in site age and parent rock.We established a total of nine study plots by choosing three topographicalunits(ridge, middle- and lower-slope) on each substrate inthe tropical lower montane forest. Pool size and supply of soil N and Pdecreased upslope on each substrate, and the magnitude of the reduction fromslope to ridge decreased in the order of Quaternary sedimentary > Tertiarysedimentary > ultrabasic rock. Between-substrate difference in soilnutrient condition was greater on the lower-slopes than the ridges.Maximum tree size decreased and stem density increased upslope on eachsubstrate. Detrended correspondence analysis demonstrated that speciescomposition also changed along topographical gradients on all substrates.However, the magnitude of topographical changes in forest structure and speciescomposition varied with substrate and decreased from Quaternary sedimentary>Tertiary sedimentary > ultrabasic rock. The greatest between-substratedifference in vegetation occurred on the lower-slopes. Accordingly, ourresults suggest that the magnitude of vegetation changes due to topographybecomes smaller with decreasing pool size and supply of nutrients.

Soil phosphorus fractionation and phosphorus-use efficiencies of tropical rainforests along altitudinal gradients of Mount Kinabalu, Borneo

Abstract We studied soil phosphorus (P) fractionation and P-use efficiencies (PUEs) of rainforests along altitudinal gradients (700–3100 m) on two types of parental rocks (sedimentary versus ultrabasic) on Mount Kinabalu, Borneo. Sedimentary rocks were known to contain more quartz (which does not adsorb P) than ultrabasic rocks. The pool (top 30 cm) of total P was always greater on sedimentary (ranging from 34.9 to 72.6 g m–2) than on ultrabasic (9.0–29.2 g m–2) rocks at comparable altitudes. Accordingly, the pools of organic P and labile inorganic P were always greater on sedimentary than on ultrabasic rocks. The pool of primary mineral, calcium P increased upslope from 1.7 to 4.3 g m–2 on sedimentary rock, suggesting that the altitudinal sequence of the sites reflected a decreasing magnitude of soil weathering upslope. The pool of calcium P on ultrabasic rock did not vary consistently with altitude (1.2–2.8 g m–2), probably reflecting the greater between-site variability of primary mineral P in parent rocks. When all sites were compared, the pool of most labile, bicarbonate-extracted inorganic P increased (ranging from 0.02 to 1.85 g m–2) with increasing calcium P. Calcium P was therefore considered to be an important P source to the biota on Kinabalu. Gross patterns in the variation of PUE (indexed as the reciprocal of the P concentration in litter) were best explained by the pool size of actively cycling P (total P minus occluded inorganic P). PUE, however, demonstrated distinct altitudinal patterns to generate an intricate conrol of P use pattern by soil P pools and altitude.

Primary succession of Hawaiian montane rain forest on a chronosequence of eight lava flows

Abstract. The primary-successional sere of a Hawaiian montane rain forest was inferred from an age sequence of eight closely located ‘a’ ā flows (clinker type lava); 8, 50, 140, ca. 300, ca. 400, ca. 1400, ca. 3000 and ca. 9000 yr, on a windward slope of Mauna Loa, Hawaii. All study sites (0.2 ha each) were at 1120 — 1250 m a.s.l. with 4000 mm mean annual rainfall. The 400-yr, 1400-yr, and 9000-yr flows had younger volcanic ash deposits, while the others were pure lava. Comparisons of tree size and foliar nutrients suggested that ash increased the availability of nitrogen, and subsequently standing biomass. An Unweighted Pair Group Cluster Analysis on the samples (flows) using quantitative vascular species composition revealed that clusters were correlated with age regardless of the substrate types (pure lava vs. ash), and an indirect ordination on the samples suggested that the sequence of sample scores along axis 1 was perfectly correlated with the age sequence. Although ash deposits increased biomass, they did not affect the sequence of the successional sere. Both pubescent and glabrous varieties of Metrosideros polymorpha (Myrtaceae) dominated upper canopy layers on all flows ≥ 50 yr and ≤ 1400 yr, but the pubescent variety was replaced by the glabrous on the flows ≥ 3000 yr. Lower layers were dominated initially by a matted fern, Dicranopteris linearis, up to 300 yr, and subsequently by tree ferns, Cibotium spp., to 9000 yr. The cover of Cibotium declined slightly after 3000 yr, while other native herb and shrub species increased. A ‘climax’ stage in the conventional sense was apparently not reached on the observed age gradient, because the sere changed continuously in biomass and species; this divergent successional phenomenon may be unique to Hawaii where the flora is naturally impoverished and disharmonic due to its geographic isolation in contrast to more diverse and harmonic floras in continents.

Nature of the "occluded" low-density fraction in soil organic matter studies: a critical review.

Abstract Density separations show great promise in elucidating the progression of organic matter decomposition and mineral association in soils. We review the literature on these separations, with a focus on the low-density material released by sonication, the so-called “occluded”, “aggregate-protected” or mineral-associated low-density fraction (m-LF). This fraction accounts for up to half of the total C in surface soils. A commonly cited model explains this material as an intermediary (between mineral-free LF and high-density fractions) during the progressive decay of plant detritus accompanied by mineral association. However, the great variance in m-LF compositions (e.g. unusual aliphaticity, high C:N, variable mean residence time) shown in the literature implies a separate genesis for some of the organic matter in this fraction in some soils. Aspects of organic particle size and lipid composition of original plant sources deserve more attention. We propose a revision of the current model that allows for materials of widely varying lability in this pool. A combination of density separation with isotope tracers, detailed chemical characterization and other physical separation techniques are needed to improve models of soil organic matter dynamics linking the density fractions.

Soil Phosphorus Fractionation and Phosphorus-Use Efficiency of a Bornean Tropical Montane Rain Forest During Soil Aging With Podozolization

We compared phosphorus (P) dynamics and plant productivity in two montane tropical rain forests (Mount Kinabalu, Borneo) that derived from similar parent materials (largely sedimentary rocks) and had similar climates but differed in terms of soil age. The younger site originated from Quaternary colluvial deposits, whereas the older site had Tertiary-age material. The older site had a distinctive spodic horizon, reduced levels of labile inorganic soil P, higher concentrations of recalcitrant organic soil P, and lower rates of net soil N mineralization. P fertilization led to soil nitrogen (N) immobilization in the P-deficient soil, indicating that soil N mineralization was limited by P at the P-deficient older site. Mean foliar nutrient concentration (on both a weight and an area basis) was similar at the two sites for all elements except P, which was lower at the older site. Aboveground net primary production (ANPP) was lower at the older site than at the younger one; this difference could be explained by the reduced availability of P and N (as down-regulated by P) at the older site. The relatively ample allocation of P and N to leaves, despite the reduced availability at the P-deficient old site, was attributable to its high resorption efficiency. High resorption resulted in lower concentrations of elements in leaf litter—that is, less decomposable low-quality litter. On the other hand, the concentration of leaf litter lignin was considerably lower at the older site; this appeared to be a de facto adaptive mechanism to avoid retarding litter decomposition.

Vegetation changes along gradients of long-term soil development in the Hawaiian montane rainforest zone

The development of the Hawaiian montane rainforest was investigated along a 4.1-million-year soil age gradient at 1200 m elevation under two levels of precipitation, the mesic (c. 2500 mm annual rainfall) vs. wet (>4000 mm) age gradient. Earlier analyses suggested that soil fertility and foliar nutrient concentrations of common canopy species changed unimodally on the same gradients, with peak values at the 20,000–150,000 yr old sites, and that foliar concentrations were consistently lower under the wet than under the mesic conditions. Our objectives were to assay the influences of soil aging and moisture on forest development using the patterns and rates of species displacements. The canopies at all sites were dominated by Metrosideros polymorpha. Mean height and dbh of upper canopy Metrosideros trees increased from the youngest site to peak values at the 2100–9000 yr sites, and successively declined to older sites. A detrended correspondence analysis applied to mean species cover values revealed that significant variation among sites occurred only on one axis (axis 1), for both soil-age gradients. Sample scores along axis 1 were perfectly correlated with soil age on the mesic gradient, and significantly correlated on the wet gradient. Higher rainfall appeared to be responsible for the higher rates of species turnover on the wet gradient probably through faster rock weathering and greater leaching of soil elements. We concluded that the changes in species cover values and size of the canopy species was a reflection of the changing pattern of nutrient availability associated with soil aging.