Ant colonization and coarse woody debris decomposition in temperate forests

Ants are ubiquitous, abundant and have widespread impacts on ecological communities and ecosystem processes. However, ant effects on coarse woody debris decomposition are unexplored. Several ant species colonize coarse woody debris for nesting, and this puts them in contact with fauna and microbes that utilize coarse woody debris as habitat and food, potentially influencing nutrient cycling and, ultimately, forest productivity. We report results from a field experiment employing 138 artificial ant nests (routed pine blocks) across five locations in southeastern US deciduous forests. We examine the correspondence between ant, termite and wood-eating fungi colonization and variation in coarse woody debris decomposition. After 1 year, nests colonized by ants had 5% more mass than those not colonized. Ant colonization corresponded with significantly less termite- and fungal-mediated decomposition of the nests. Without ants, termites removed 11.5% and fungi removed 4% more wood biomass. Ants, termites and wood-eating fungi all colonized pine nests where temperatures were highest, and ants also preferred higher soil moisture whereas termites and fungi responded negatively to high soil moisture when temperatures were higher. Ants reduce termite colonies through predation, and may inhibit fungi through the secretion of antimicrobial compounds. Our results indicate that interactions between forest understory ants, termites and fungi may influence the rate of coarse woody debris decomposition—biotic interactions that potentially influence forest structure and function.     

Woody Debris in the Mangrove Forests of South Florida1

Woody debris is abundant in hurricane‐impacted forests. With a major hurricane affecting South Florida mangroves approximately every 20 yr, carbon storage and nutrient retention may be influenced greatly by woody debris dynamics. In addition, woody debris can influence seedling regeneration in mangrove swamps by trapping propagules and enhancing seedling growth potential. Here, we report on line‐intercept woody debris surveys conducted in mangrove wetlands of South Florida 9–10 yr after the passage of Hurricane Andrew. The total volume of woody debris for all sites combined was estimated at 67 m³/ha and varied from 13 to 181 m³/ha depending upon differences in forest height, proximity to the storm, and maximum estimated wind velocities. Large volumes of woody debris were found in the eyewall region of the hurricane, with a volume of 132 m³/ha and a projected woody debris biomass of approximately 36 t/ha. Approximately half of the woody debris biomass averaged across all sites was associated as small twigs and branches (fine woody debris), since coarse woody debris >7.5 cm felled during Hurricane Andrew was fairly well decomposed. Much of the small debris is likely to be associated with post‐hurricane forest dynamics. Hurricanes are responsible for large amounts of damage to mangrove ecosystems, and components of associated downed wood may provide a relative index of disturbance for mangrove forests. Here, we suggest that a fine:coarse woody debris ratio ≤0.5 is suggestive of a recent disturbance in mangrove wetlands, although additional research is needed to corroborate such findings.     

Aquatic Macrophytes Alter Metabolism and Nutrient Cycling in Lowland Streams

Macrophytes influence the physical, chemical, and biological characteristics of lowland streams, so may be critically important in stream management. We investigated the role of macrophytes in regulating metabolism and nutrient cycling in three lowland, agricultural streams. We measured stream metabolism over the growing season and following experimental macrophyte removal, and used short-term nutrient additions of phosphate (P) and ammonium to assess macrophyte influences on nutrient uptake. Primary production was closely correlated with macrophyte cover across all streams and dates, and decreased greatly with macrophyte removal, whereas ecosystem respiration was not correlated with macrophyte cover and was not altered by macrophyte removal. Phosphate uptake velocity was negatively related to primary production, suggesting that macrophyte activity actually slowed P uptake. Ammonium uptake was not correlated with macrophyte cover or metabolism metrics. Stream nitrate concentrations typically exceeded concentrations of incoming groundwater, suggesting little net nitrate retention in these macrophyte-dominated streams. Phosphorous demand by macrophytes was 10-fold lower than observed uptake rates, indicating that macrophyte P demand was much lower than that of other stream biota. Nitrogen demand by macrophytes was nearly equal to ammonium uptake and was not sufficient to affect the high nitrate flux. These results indicate that macrophytes drive ecosystem metabolism but have limited influence on water column nutrient concentrations because macrophyte demand is much lower than the supply available from the water column. Thus macrophytes in our streams had a large impact on stream trophic state, but offered little potential to influence nutrient removal via management.     

Effects of wood removal on stream habitat and nitrate uptake in two northeastern US headwater streams

Forested headwater streams play an important role in watershed nutrient dynamics, and wood is thought to be a key factor influencing habitat structure and nitrate-nitrogen dynamics in many forested streams. Because wood in streams can promote nitrogen uptake through denitrification, we hypothesized that nitrate uptake velocities would decrease following wood removal. We measured stream characteristics and nitrate uptake velocities before and after wood manipulation experiments conducted at Hubbard Brook Experimental Forest, NH, and the Sleepers River watershed, VT. The mean size of stream substrates and the amount of riffle habitat increased following wood removal. In contrast to our expectations, summer nitrate uptake velocities increased in the wood removal treatments relative to the reference treatments, possibly because wood removal increased the availability of stable substrates for periphyton growth, therefore increasing nitrate demand in these streams. Our results highlight that effects of wood on stream ecosystems occur through multiple pathways and suggest that the relative importance of these pathways may vary seasonally.     

Evaporation as a nutrient retention mechanism at Sycamore Creek,Arizona

Studies of nutrient cycling in streams have typically focused on patterns and mechanisms of retention because retention can result in temporary or permanent removal of biologically important nutrients. Biogeochemical studies of nitrate in stream ecosystems have focused primarily on biotic uptake and sequestration, while little is known about abiotic mechanisms of nitrogen retention. Evaporation is one abiotic mechanism that can contribute to nutrient retention with nutrients stored as precipitated solutes in sandbars. The objective of this study was to assess the significance of evaporation-driven nitrate retention in sandbars to reach-scale nutrient budgets at Sycamore Creek, Arizona. The vertical profile of chloride and nitrate evaporties were used as a tool to evaluate abiotic retention. I found that salts accumulated in surface layers (0–2 cm) of exposed sandbar sediments. Calculated evaporative retention rate was 0.7–5.4% of average rate of uptake by biota in the surface stream. However, the area of influence of these two mechanisms varies greatly. Taking into account this spatial and seasonal variation in areal extent of the surface stream versus exposed sandbar surfaces, evaporite formation accounted for 14.8% of retention in the study reach and up to 46.0% of annual retention compared to instream biotic uptake. Nitrate retention via evaporation is important because of the temporary disconnection of nutrients stored in sandbars to the surface stream delaying further biological processing until hydrological reconnection occurs. Handling editor: D. Ryder     

Nutrient uptake in eastern deciduous tree seedlings

Tree seedlings that colonize large treefall gaps are generally shade-intolerant species with high potential relative growth rates. Nutrient availability may be significantly elevated in disturbance-induced gaps, however, little is known about the role of differences in nutrient uptake capacities of different species in structuring the community response to gap openings in eastern North American deciduous forests. Seven tree species were grown from seed under both a high and a low nutrient regime, and uptake kinetics of phosphate, ammonium, and nitrate were studied. Yellow birch, a species with intermediate shade tolerance and relative growth rate, had the highest maximum rates of uptake of all ions, while tulip tree, a gap-colonizing species with high relative growth rate, had the lowest rate of phosphate uptake and intermediate rates of ammonium and nitrate uptake. Beech and hickory, which have low relative growth rates and are not gap-colonizing species, had intermediate levels of nutrient uptake. There was no evidence that species with the highest maximum uptake rates measured at high supply concentrations had relatively low uptake at low nutrient supply concentrations. Although birch increased phosphate absorption capacity when grown under a low nutrient regime, this pattern did not hold for nitrate or ammonium uptake, and other species showed no change in nutrient uptake capacity according to nutrient growth regime. Clearly, factors other than nutrient absorption capacity, such as nutrient use efficiency or allocation to root vs. shoot biomass, underlie differences in species' capacities to colonize and maintain a high relative growth rate in canopy gaps.     

Diversity of wood-inhabiting Agaricomycotina on wood of different size classes in riparian forests of Uruguay

Many Agaricomycotina species are saprobes, playing a fundamental role in nutrient cycling in forest ecosystems by decomposing wood. Little is known about factors affecting diversity of wood-inhabiting fungi in the neotropical, warm temperate native forests of Uruguay. Most of these native forests are riparian harboring about 300 tree species. In this study, we assessed the diversity of wood-inhabiting fungi on wood of different size classes in riparian forests of Uruguay. We recovered 186 species of Agaricomycotina, including 113 corticioid and 58 polyporoid taxa. Eleven taxa accounted for 38% of the all the samples. The highest number of species was found on fine woody debris (FWD, 2–10 cm diam) than coarse woody debris (CWD, >10 cm diam) and very fine woody debris (VFWD, <2 cm diam). Species-accumulation curves did not reach an asymptote for any of the groups or wood diameter classes studied. Polyporoids were more frequently recorded on CWD (61% of collections) and corticioids on VFWD (77%). Species richness estimated by non-parametric estimators indicates an Agaricomycotina species richness between 450 and 700 taxa. Our results show that Uruguayan riparian forests, despite its limited area and fragmentation, support a wood-inhabiting Agaricomycotina diversity comparable to less fragmented forests with more plant diversity.     

Woody Debris Amendment Enhances Reclamation after Oil Sands Mining in Alberta,Canada

Mining disturbs large forested areas around the world, including boreal forests after oil sands mining in Canada. Industrial companies are expected to reclaim degraded land to ecosystems with equivalent land capability. This research showed the value of woody debris for reclamation of dramatically disturbed landscapes with a forest ecosystem end land use. Adding woody debris during reclamation can facilitate recovery of flora, soil nutrient cycling and water and nutrient holding capacity. Combined with forest floor material, woody debris can provide native plant propagules that would be otherwise commercially unavailable. Sites with and without woody debris on forest floor material containing identifiable litter (L), fragmented and fermented litter (F), and humus (H) (LFH), and peat mineral soil mix (peat) cover soils were studied. Within 2 years, woody debris decreased bare ground and created microsites which were positively associated with greater vegetation cover and woody plant density. Woody debris treatments had lower soil available nitrate and soil under woody debris had a lower temperature range and higher soil volumetric water content than control treatments without woody debris. Woody debris did not affect first year microbial biomass carbon or mycorrhizae, but both were greater on LFH than peat cover soil. LFH was associated with lower bare ground and greater vegetation cover, species richness, and soil phosphorus and potassium than peat cover soil, which had greater soil sulfate .     

NITRATE AND PHOSPHATE UPTAKE INTERACTIONS IN A MARINE PRYMNESIOPHYTE1

The short- and long-term uptake of nitrate and phosphate ions, and their interactions, were studied as functions of the preconditioning of Pavlova lutheri (Droop) Green. Populations were preconditioned in continuous culture at a variety of growth rates and N:P supply ratios. The maximum uptake rates cell^?1 for nitrate and phosphate were of similar magnitudes, in spite of the forty-fold smaller requirement for phosphorus. Short-term phosphate uptake was independent of the nitrate concentration, but the short-term nitrate uptake rate was reduced in the presence of phosphate. The severity of inhibition of nitrate uptake by phosphate was positively correlated with the preconditioning N:P supply ratio and the preconditioning growth rate. In response to large additions of nutrients, P. lutheri was able to increase its phosphorus content sixty-fold, but was only able to take up enough nitrate to double its nitrogen content. The high rate of phosphate uptake relative to its requirement, the inhibition of nitrate uptake by phosphate, and the large capacity for phosphorus storage relative to its requirement, all of which were observed even under N limitation, may imply that even where nitrogen is limiting there can be interspecific competition for available phosphate.     

Nitrogen and phosphorus uptake in two Idaho (USA) headwater wilderness streams

Nitrate and phosphate solutions were released into two reaches of two central Idaho streams to determine within- and between-stream variability in uptake lengths, uptake rates, and mass transfer coefficients. Physical and biotic stream characteristics and periphyton nitrate-uptake rates in recirculating chambers were measured to determine their influence on nutrient dynamics. Phosphate uptake length did not differ among the four reaches. There were no within-stream differences in nitrate uptake lengths but they did differ between the two streams. Long nitrate uptake lengths likely were due to instream concentrations above saturation but also may have been influenced by differences in active surface area and algal abundance. Nitrate and phosphate uptake lengths were longer, and uptake rates higher, than most other published values. However, mass transfer coefficients were comparable to measurements in other streams. Mass transfer coefficients may be a better parameter for temporal and spatial comparisons of instream nutrient dynamics, and for determining the underlying causes of variability in uptake length. Received: 27 May 1998 / Accepted: 11 January 1999     

Comparisons of the Colonisation by Invertebrates of Three Species of Wood,Alder Leaves,and Plastic “Leaves” in a Temperate Stream

Small woody debris in streams is abundant, and may be a food source or may provide a substrate on which other food sources such as biofilm may develop, both of which may be significant to invertebrates in times of food scarcity. We examined patterns of invertebrate colonisation of small woody debris (veneers of red alder, Douglas‐fir, and western red cedar), red alder leaves, and plastic (as an inert substrate to mimic leaves). Invertebrate colonisation was high on alder leaves, but low on wood substrates and plastic, controlling for the available surface area. Detritivorous invertebrates had significantly higher colonisation rates of alder leaves versus the other four substrates, whereas predators and collectors did not (consistent with their use of these as substrates and not food). All wood decreased in mass by <15% and leaves by ∼50% over the 75 days of the experiment. For all taxa tested, there was no significant difference in their colonisation of the wood veneers versus the plastic sheets. These results suggest that wood was not directly used by these invertebrates as a food source, or that there could be similar biofilm development on the surfaces of these substrates. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

腐烂等级和径级对天宝岩长苞铁杉林木质残体理化性质的影响

木质残体是森林生态系统的重要组成部分,其理化性质影响木质残体的分解.本研究以集中分布于天宝岩国家级自然保护区的长苞铁杉(Tsuga longibracteata)林木质残体为对象,将4个不同类型林分的木质残体划分为5个腐烂等级和4个径级,研究林分类型、腐烂等级、径级及其交互作用对木质残体理化性质的影响.结果 表明:从物...     

Woody Vegetation Removal Stimulates Riparian and Benthic Denitrification in Tallgrass Prairie

Expansion of woody vegetation into areas that were historically grass-dominated is a significant contemporary threat to grasslands, including native tallgrass prairie ecosystems of the Midwestern United States. In tallgrass prairie, much of this woody expansion is concentrated in riparian zones with potential impacts on biogeochemical processes there. Although the effects of woody riparian vegetation on denitrification in both riparian soils and streams have been well studied in naturally wooded ecosystems, less is known about the impacts of woody vegetation encroachment in ecosystems that were historically dominated by herbaceous vegetation. Here, we analyze the effect of afforestation and subsequent woody plant removal on riparian and benthic denitrification. Denitrification rates in riparian soil and selected benthic compartments were measured seasonally in naturally grass-dominated riparian zones, woody encroached riparian zones, and riparian zones with woody vegetation removed in two separate watersheds. Riparian soil denitrification was highly seasonal, with the greatest rates in early spring. Benthic denitrification also exhibited high temporal variability, but no seasonality. Soil denitrification rates were greatest in riparian zones where woody vegetation was removed. Additionally, concentrations of nitrate, carbon, and soil moisture (indicative of potential anoxia) were greatest in wood removal soils. Differences in the presence and abundance of benthic compartments reflected riparian vegetation, and may have indirectly affected denitrification in streams. Riparian soil denitrification increased with soil water content and NO₃ ^?. Management of tallgrass prairies that includes removal of woody vegetation encroaching on riparian areas may alter biogeochemical cycling by increasing nitrogen removed via denitrification while the restored riparian zones return to a natural grass-dominated state.     

Vertical pattern and its driving factors in soil extracellular enzyme activity and stoichiometry along mountain grassland belts

Headwater streams are foci for nutrient and energy loading from terrestrial landscapes, in situ nutrient transformations, and downstream transport. Despite the prominent role that headwater streams can have in regulating downstream water quality, the relative importance of processes that can influence nutrient uptake have not been fully compared in heterotrophic aquatic systems. To address this research need, we assessed the seasonality of dissolved organic carbon (DOC) and nitrate (NO₃^?) uptake, compared the relative influence of hydrologic and biogeochemical drivers on observed seasonal trends in nutrient uptake, and estimated the influence of these biological transformations on watershed scale nutrient retention and export. We determined that seasonal reductions in DOC and NO₃^? concentrations led to decreases in the potential for the biotic community to take up nutrients, and that seasonality of DOC and NO₃^? uptake was consistent with the seasonal dynamics of ecosystem metabolism. We calculated that that during the post-snowmelt period (June to August), biotic retention of both dissolved organic carbon and nitrate exceeded export fluxes from this headwater catchment, highlighting the potential for biological processes to regulate downstream water quality.     

Greater phosphorus uptake in forested headwater streams modified by clearfell forestry

Clearfell, burn and sow (CBS) forestry can potentially alter stream environments by increasing available light and the input of woody debris. However, little is known about how CBS forestry affects in-stream processes such as nutrient uptake. We evaluate whether short-term (2–7 years) environmental changes (e.g. light availability and woody debris) associated with CBS forestry lead to differences in nutrient uptake metrics. To do this, we measured in-stream uptake of soluble reactive phosphorus (SRP) and ammonium (NH₄) in three old growth (OG) and four CBS-affected headwater stream reaches. The abundance of fine woody debris and light availability were significantly greater in CBS-affected than in OG reaches. Uptake velocities varied from 0.0880 to 0.951 mm min^?1 for NH₄ and from 0.0383 to 1.06 mm min^?1 for SRP across all sites. The mean uptake of SRP, but not NH₄, was significantly greater (i.e. higher uptake velocities and lower uptake lengths) in CBS-affected than in OG reaches. These results suggest that CBS forestry altered the stream environment enabling greater SRP uptake relative to OG reaches. Our findings highlight the tight linkage between headwater streams and their surrounding terrestrial environment, which has direct implications for catchment-scale biogeochemical processes.     

Effect of decomposing post-fire coarse woody debris on soil fertility and nutrient availability in a Mediterranean ecosystem

Post-fire coarse woody debris can represent a valuable nutrient reservoir for a regenerating ecosystem, helping to prevent soil fertility losses after a wildfire. However, there is scarce information on its effect on soil nutrient cycling and availability. We established three study sites along an altitudinal gradient in a burnt pine forest (SE Spain). At each site we determined: (1) decomposition rates and nutrient dynamics in charred logs left on the ground, 2 and 4 years after the fire, and (2) available nutrients in the soil and in the microbial fraction below charred logs and in bare soil areas. Despite the relatively slow decay rates in this Mediterranean climate (ca. 10 % of dry weight lost after 4 years), N and P were progressively released by logs, accounting for ca. 40 and 65 % of the initial content respectively after 4 years. This implies that the total aboveground biomass of the burnt forest released around 20 kg ha^?1 of N and 2 kg ha^?1 of P during this period. The presence of post fire coarse woody debris consistently increased soil organic matter by around 18 %, total C and N by 42 and 26 %, respectively, dissolved organic C and N by 47 %, available inorganic P by 68 %, and microbial biomass and nitrogen by some 36 and 48 %, respectively. By contrast, soil bulk density decreased by ca. 18 % under logs compared to bare areas. Thus, the fire-killed wood was useful in the recovery of soil fertility and nutrient availability. Leaving the post-fire woody debris on site can enhance the biogeochemical sustainability, microbiological processes and soil ecological functioning. The detrimental effect of post-fire salvage logging on soil fertility should be therefore considered when making management decisions.     

Nutrient uptake in streams draining agricultural catchments of the midwestern United States

1. Agriculture is a major contributor of non‐point source pollution to surface waters in the midwestern United States, resulting in eutrophication of freshwater aquatic ecosystems and development of hypoxia in the Gulf of Mexico. Agriculturally influenced streams are diverse in morphology and have variable nutrient concentrations. Understanding how nutrients are transformed and retained within agricultural streams may aid in mitigating increased nutrient export to downstream ecosystems. 2. We studied six agriculturally influenced streams in Indiana and Michigan to develop a more comprehensive understanding of the factors controlling nutrient retention and export in agricultural streams using nutrient addition and isotopic tracer studies. 3. Metrics of nutrient uptake indicated that nitrate uptake was saturated in these streams whereas ammonium and phosphorus uptake increased with higher concentrations. Phosphorus uptake was likely approaching saturation as evidenced by decreasing uptake velocities with concentration; ammonium uptake velocity also declined with concentration, though not significantly. 4. Higher whole‐stream uptake rates of phosphorus and ammonium were associated with the observed presence of stream autotrophs (e.g. algae and macrophytes). However, there was no significant relationship between measures of nutrient uptake and stream metabolism. Water‐column nutrient concentrations were positively correlated with gross primary production but not community respiration. 5. Overall, nutrient uptake and metabolism were affected by nutrient concentrations in these agriculturally influenced streams. Biological uptake of ammonium and phosphorus was not saturated, although nitrate uptake did appear to be saturated in these ecosystems. Biological activity in agriculturally influenced streams is higher relative to more pristine streams and this increased biological activity likely influences nutrient retention and transport to downstream ecosystems.     

Nutrient utilisation by shallow water temperate sponges in New Zealand

Major nutrients such as phosphate, nitrate, ammonium and silicate, are involved in the metabolic processes of marine organisms. Sponges take up and produce inorganic nutrients and the extent at which they affect the budgets available for other organisms has received little attention. For this reason, we investigated nutrient fluxes for several sponge species in order to estimate whether sponges were net producers or consumers of nutrients from the water column, and how these patterns changed over time. Nutrient fluxes were examined on the south coast of Wellington, New Zealand. For the nutrient analysis (nitrate, nitrite, ammonium, phosphate and silicate), water samples were collected in situ from the inhalant and exhalant water of different sponge species. Samples were analysed both in a multi-species survey and over a two-year period for three other species to determine any temporal changes in fluxes. Our results yielded significant differences in nutrient concentrations between the inhalant and exhalant water for some of the species, but there was no clear pattern associated with the time of year. The levels of dissolved inorganic nutrients in the ambient water varied considerably over the 2-year study period. It is possible that a lack of a clear pattern of nutrient uptake/release of nutrients in some of the study species, and the fact that not all species showed significant uptake/release at different times of the year, may be related to high levels of temporal and spatial variation in the ambient nutrient availability, as well as other temporal fluctuations in parameters, such as water temperature, sponge size, and concentration of food in the water column. Finally, we believe that the activity of specific microbial communities associated with these sponges may be important in explaining the fluxes we have reported.     

Nitrogen and phosphorus dynamics in hot desert streams of Southwestern U.S.A.

Nitrogen to phosphorus ratios and concentrations of nitrate and soluble reactive phosphate are presented for an array of Southwestern streams as evidence that nitrogen is the limiting nutrient where such limitation occurs. Nitrate uptake in sections of intermittent streams was attributable to autotrophic activity. Uptake of soluble reactive phosphate was unrelated to any indicator of autotrophic activity, thus concentrations of this nutrient in desert and semi-desert stream waters may be controlled by other factors.     

Control of Net Uptake of Nutrients by Regulation of Influx in Barley Plants Recovering from Nutrient Deficiency

Rates of influx and net uptake of nitrate, phosphate and sulphatewere measured in intact barley plants, and concurrent effluxwas obtained by difference. Net uptake of these anions variedwidely depending on the nutrient status of the plants, and thedifferences in net uptake could be accounted for almost entirelyby changes in influx. Efflux played only a minor role in regulatingnet uptake of nitrate, phosphate or sulphate during recoveryfrom N-, P-, or S-deficiency. Nitrate influx and short-term ammonium absorption by N-deficientbarley plants were closely correlated, and varied in parallelwith rates of net uptake of nitrate or ammonium by similar plants.Again, it would seem that net uptake of ammonium is controlledpredominantly by changes in the rate of influx.Copyright 1993,1999 Academic Press Hordeum vulgare, barley, nutrient absorption, influx, nitrate, phosphate, sulphate, ammonium