Moss Water Research Articles

Photosynthetic microorganisms effectively contribute to bryophyte CO2 fixation in boreal and tropical regions

Photosynthetic microbes are omnipresent in land and water. While they critically influence primary productivity in aquatic systems, their importance in terrestrial ecosystems remains largely overlooked. In terrestrial systems, photoautotrophs occur in a variety of habitats, such as sub-surface soils, exposed rocks, and bryophytes. Here, we study photosynthetic microbial communities associated with bryophytes from a boreal peatland and a tropical rainforest. We interrogate their contribution to bryophyte C uptake and identify the main drivers of that contribution. We found that photosynthetic microbes take up twice more C in the boreal peatland (~4.4 mg CO2.h−1.m−2) than in the tropical rainforest (~2.4 mg CO2.h−1.m−2), which corresponded to an average contribution of 4% and 2% of the bryophyte C uptake, respectively. Our findings revealed that such patterns were driven by the proportion of photosynthetic protists in the moss microbiomes. Low moss water content and light conditions were not favourable to the development of photosynthetic protists in the tropical rainforest, which indirectly reduced the overall photosynthetic microbial C uptake. Our investigations clearly show that photosynthetic microbes associated with bryophyte effectively contribute to moss C uptake despite species turnover. Terrestrial photosynthetic microbes clearly have the capacity to take up atmospheric C in bryophytes living under various environmental conditions, and therefore potentially support rates of ecosystem-level net C exchanges with the atmosphere.

Peat depth as a control onSphagnummoisture stress during seasonal drought

AbstractPeatlands are globally important long‐term sinks of carbon, however there is concern that enhanced peat decomposition and moss moisture stress due to climate change mediated drought will reduce moss productivity making these ecosystems vulnerable to carbon loss and associated long‐term degradation. Peatlands are resilient to summer drought moss stress because of negative ecohydrological feedbacks that generally maintain a wet peat surface, but where feedbacks may be contingent on peat depth. We tested this ‘survival of the deepest’ hypothesis by examining water table (WT) position, near‐surface moisture content, and soil water tension in peatlands that differ in size, peat depth, and catchment area during a summer drought. All shallow sites (<40 cm depth) lost their WT (i.e., the groundwater well was dry) for considerable time during the drought period. Near‐surface soil water tension increased dramatically at shallow sites following WT loss, increasing ~5–7.5× greater at shallow sites compared to deep sites (≥40 cm depth). During a mid‐summer drought intensive field survey, we found that 60–67% of plots at shallow sites exceeded a 100 mb tension threshold used to infer moss water stress. Unlike the shallow sites, tension typically did not exceed this 100 mb threshold at the deep sites. Using species dependent water content – chlorophyll fluorescence thresholds and relations between volumetric water content and WT depth, Monte Carlo simulations suggest that moss had nearly twice the likelihood of being stressed at shallow sites (0.38 ± 0.24) compared to deep sites (0.22 ± 0.18). This study provides evidence that mosses in shallow peatland may be particularly vulnerable to warmer and drier climates in the future, but where species composition may play an important role. We argue that a critical ‘threshold’ peat depth specific for different hydrogeological and hydroclimatic regions can be used to assess what peatlands are especially vulnerable to climate change mediated drought.

Effects of Brachythecium plumosum and Plagiomnium venustum on seed germination and seedling growth of invasive plants

Invasive plants can inhibit the survival and reproduction of native species through alle-lopathy. It is not clear whether the native plants, especially the mosses in the ground layer, inf-luence the invasive plants. In this study, we examined the effects of two native moss species, Brachythecium plumosum and Plagiomnium venustum, on two malignant invasive plants, Echinochloa crusgalli and Daucus carota. The effects of mosses on seed germination and seedling growth of both invasive species were determined based on the clump structure and allelopathy of the mosses. The germination rate, germination potential and germination index of the two invasive species were significantly inhibited when seeds fallen on or into the moss clump, with an order of inhibition effect: above moss clump>below moss clump>no moss. Radicle length and radicle/plumule of D. Carota were significantly affected when seeds fallen into the moss clump. Moss water extracts significantly reduced germination rate, germination potential, and germination index of the two invasive plants, with these effects being concentration-dependent. To some extent, moss water extracts increased the plumule length, radicle length and radicle/plumule of D. Carota seedlings, but without effect on E. crusgalli. Both mosses showed inhibitory effects on seed germination and seedling growth of two invasive plants, with higher sensitivity of E. crusgalli than D. Carota. Along with the increases in concentration of water extract, stronger inhibitory effects were found. Therefore, mosses could partially inhibit seed germination and seedling growth of invasive plants.

Effect of climate and moss vegetation on ground surface temperature and the active layer among different biogeographical regions in Antarctica

Ground surface temperature (GST) and active layer thickness (ALT) are key indicators of climate change (CC) in permafrost regions, with their relationships with climate and vegetation being crucial for the understanding of future climate change scenarios, as well as of CC feedbacks on the carbon cycle and water balance.Antarctic ice free-areas host simplified ecosystems with vegetation dominated by mosses and lichens, and an almost negligible anthropogenic impact, providing a good template of ecosystem responses to CC. At three different Antarctic Conservation Biogeographical Regions (ACBR) sites in Antarctica located between 74° and 60°S, we compared barren ground and moss vegetated sites to understand and quantify the effects of climate (air temperature and incoming radiation) and of vegetation on GST and ALT. Our data show that incoming radiation is the most important driver of summer GST at the southernmost site, while in the other sites air temperature is the main driver of GST. Our data indicate that there is a decoupling between ALT and summer GST, because the highest GST values correspond with the thinnest ALT. Moreover, our data confirm the importance of the buffering effect of moss vegetation on GST in Antarctica. The intensity of the effect of moss cover on GST and ALT mainly depends on the species-specific moss water retention capacity and on their structure. These results highlight that the correct assessment of the moss type and of its water retention can be of great importance in the accurate modelling of ALT variation and its feedback on CC.

MODEL PENGOLAHAN AIR GAMBUT MENJADI AIR MINUM BERBASIS MASYARAKAT

Research about model of peat moss water processing become drinking water based on society is used to eliminate organic matter, chemical elements which are Fe, TDS, Zn, Flurida, NO3, and NO2 and pH. This model has purpose to find the solution about the supply of drinking water properly and simply to household and society. This research is conducted in Sub District Johan Pahlawano, West Aceh, exactly in the society surrounded by peat moss water area. This is experimental research which uses model of filtering tools of peat moss water, with the medias are sand, gravel, charcoal from coconut shell, then are filled in PVC pipe with up flow system. The samples are used 3 water samples from vary villages surrounded the circle of Teuku Umar University that contain peat moss waters, those are Cot Lawang, Rundeng and Seunebok. The research result with experimental method by Simple Plan from PVC pipe appropriates with Standard Work Of Clean Water for the parameter of Fe, TDS, Zn, Flurida, NO3, dan NO2 based on PERMENKES RI No. 907 of 2002. But for the pH, the result cannot reach that standard. So, it needs to improve the engineering model to reach the perfect result. Thus, the engineering tools can be applied in the society with water supply problem, especially in peat moss water area. However, this water result is only used to the need except as drinking water.

PENINGKATAN KUALITAS AIR SUNGAI UNTUK IRIGASI PERSAWAHAN PADI DENGAN SISTEM “KONTROL pH” DI KABUPATEN BENGKALIS, RIAU

Bengkalis district has a population of 690,366 people spread in the area of 11,481.77 Km2. Natural resources potencial in this area is quite large, so that local Government has a high commitment to meet the demand of local food, and even regional. To implement this goal, local government will build irrigation systems to irrigate 1,500 ha of rice field land which decrease of water in dry season. However, there are some constraints experienced are : the river for irrigation water source is located near the beach, so it is influenced by tidal sea water. Besides, the peat moss water contains a high organic matter and acid. To solve this problem, we need to treat the river water for irrigation, so that its quality meets the requirement for agriculture. While tidal conditions can be set with the pumping time. From the results of the research in the laboratory showed that the river water pH = 4 while the river water quality standard for the rice field is the appropriate 5 - 9 mg/l. Therefore, the required water treatment to raise pH to comply with the standard quality of water for agriculture. Research conducted in the village Langkat, district Siak Kecil. This activity includes laboratory research, design creation tool to increase pH river water irrigation, tools development, up to the trials and monitoring. Keywords : Peningkatan Kualitas Air, Irigasi Persawahan, Kontrol pH

The evolution of the stomatal apparatus: intercellular spaces and sporophyte water relations in bryophytes-two ignored dimensions.

Cryo-scanning electron microscopy shows that nascent intercellular spaces (ICSs) in bryophytes are liquid-filled, whereas these are gas-filled from the outset in tracheophytes except in the gametophytes of Lycopodiales. ICSs are absent in moss gametophytes and remain liquid-filled in hornwort gametophytes and in both generations in liverworts. Liquid is replaced by gas following stomatal opening in hornworts and is ubiquitous in moss sporophytes even in astomate taxa. New data on moss water relations and sporophyte weights indicate that the latter are homiohydric while X-ray microanalysis reveals an absence of potassium pumps in the stomatal apparatus. The distribution of ICSs in bryophytes is strongly indicative of very ancient multiple origins. Inherent in this scenario is either the dual or triple evolution of stomata. The absence, in mosses, of any relationship between increases in sporophyte biomass and stomata numbers and absences, suggests that CO2 entry through the stomata, possible only after fluid replacement by gas in the ICSs, makes but a minor contribution to sporophyte nutrition. Save for a single claim of active regulation of aperture dimensions in mosses, all other functional and structural data point to the sporophyte desiccation, leading to spore discharge, as the primeval role of the stomatal apparatus.This article is part of a discussion meeting issue 'The Rhynie cherts: our earliest terrestrial ecosystem revisited'.

Peat depth as a control on moss water availability under evaporative stress

AbstractNorthern peatlands are a vital component of the global carbon cycle, containing large stores of soil organic carbon and acting as a long‐term carbon sink. Moss productivity is an important factor in determining whether these wetlands will retain this function under future climatic conditions. Research on unsaturated water flow in peatlands, which controls moss productivity during periods of evaporative stress, has focused on relatively deep bog systems. However, shallower peatlands and marginal connective wetlands can be essential components of many landscape mosaics. In order to better understand factors influencing moss productivity, water balance simulations using HYDRUS‐1D were run for different soil profile depths, compositions, and antecedent moisture conditions. Our results demonstrate a bimodal distribution of peatland realizations, either primarily conserving water by limiting evapotranspiration or maximizing moss productivity. For sustained periods of evaporative stress, both deep water storage and a shallow initial water table delay the onset of high vegetative stress, thus maximizing moss productivity. A total depth of sand and peat of 0.8 m is identified as the threshold above which increasing peat depth has no effect on changing vegetative stress response. In contrast, wetlands with shallow peat deposits (less than 0.5 m thick) are least able to buffer prolonged periods of evaporation due to limited labile water storage and will thus quickly experience vegetative stress and so limit evaporation and conserve water. With a predicted increase in the frequency and size of rain events in continental North America, the moss productivity of shallow wetland systems may increase, but also greater moisture availability will increase the likelihood they remain as wetlands in a changing climate.

Peatland water repellency: Importance of soil water content, moss species, and burn severity

Wildfire is the largest disturbance affecting peatlands, with northern peat reserves expected to become more vulnerable to wildfire as climate change enhances the length and severity of the fire season. Recent research suggests that high water table positions after wildfire are critical to limit atmospheric carbon losses and enable the re-establishment of keystone peatland mosses (i.e. Sphagnum). Post-fire recovery of the moss surface in Sphagnum-feathermoss peatlands, however, has been shown to be limited where moss type and burn severity interact to result in a water repellent surface. While in situ measurements of moss water repellency in peatlands have been shown to be greater for feathermoss in both a burned and unburned state in comparison to Sphagnum moss, it is difficult to separate the effect of water content from species. Consequently, we carried out a laboratory based drying experiment where we compared the water repellency of two dominant peatland moss species, Sphagnum and feathermoss, for several burn severity classes including unburned samples. The results suggest that water repellency in moss is primarily controlled by water content, where a sharp threshold exists at gravimetric water contents (GWC) lower than ∼1.4gg−1. While GWC is shown to be a strong predictor of water repellency, the effect is enhanced by burning. Based on soil water retention curves, we suggest that it is highly unlikely that Sphagnum will exhibit strong hydrophobic conditions under field conditions.

Including hydrological self-regulating processes in peatland models: Effects on peatmoss drought projections.

The water content of the topsoil is one of the key factors controlling biogeochemical processes, greenhouse gas emissions and biosphere - atmosphere interactions in many ecosystems, particularly in northern peatlands. In these wetland ecosystems, the water content of the photosynthetic active peatmoss layer is crucial for ecosystem functioning and carbon sequestration, and is sensitive to future shifts in rainfall and drought characteristics. Current peatland models differ in the degree in which hydrological feedbacks are included, but how this affects peatmoss drought projections is unknown. The aim of this paper was to systematically test whether the level of hydrological detail in models could bias projections of water content and drought stress for peatmoss in northern peatlands using downscaled projections for rainfall and potential evapotranspiration in the current (1991-2020) and future climate (2061-2090). We considered four model variants that either include or exclude moss (rain)water storage and peat volume change, as these are two central processes in the hydrological self-regulation of peatmoss carpets. Model performance was validated using field data of a peatland in northern Sweden. Including moss water storage as well as peat volume change resulted in a significant improvement of model performance, despite the extra parameters added. The best performance was achieved if both processes were included. Including moss water storage and peat volume change consistently reduced projected peatmoss drought frequency with >50%, relative to the model excluding both processes. Projected peatmoss drought frequency in the growing season was 17% smaller under future climate than current climate, but was unaffected by including the hydrological self-regulating processes. Our results suggest that ignoring these two fine-scale processes important in hydrological self-regulation of northern peatlands will have large consequences for projected climate change impact on ecosystem processes related to topsoil water content, such as greenhouse gas emissions.

Machine Vision Optimization using Nature-Inspired Algorithms to Model Sunagoke Moss Water Status

Machine vision has been widely implemented to monitor water status of plants. The performance of machine vision affects the prediction process of plant water status. Therefore optimization is needed to improve the performance of machine vision. The objective of this study is to optimize the performance of machine vision to model Sunagoke moss water status. Back Propagation Neural Network was used to model the relationship of image features and Sunagoke moss water status. Multi Objective Optimization (MOO) was used to select 212 image features to get maximum prediction accuracy and minimum number of features subset. Nine nature-inspired algorithms for optimization i.e . Genetic Algorithms (GAs), Discrete Particle Swarm Optimization (DPSO), Honey Bees Mating Optimization (HBMO), Simulated Annealing (SA), Ant Colony Optimization (ACO), Intelligent Water Drops (IWD), Discrete Firefly Algorithm (DFA), Discrete Hungry Roach Infestation Optimization (DHRIO), and Fish Swarm Intelligent (FSI) were compared. The result shows generally that the prediction model using feature selection techniques achieved significant prediction accuracy, and the number of feature-subset, and was better than the model without feature selection to predict Sunagoke moss water status.

Hydrogeological controls on post-fire moss recovery in peatlands

Summary Wildfire is the largest disturbance affecting boreal peatlands, however, little is known about the controls on post-fire peatland vegetation recovery. While small-scale variation in burn severity can reduce post-fire moss water availability, high water table (WT) positions following wildfire are also critical to enable the re-establishment of keystone peatland mosses ( i.e. Sphagnum ). Thus, post-fire moss water availability is also likely a function of landscape-scale controls on peatland WT dynamics, specifically, connectivity to groundwater flow systems ( i.e. hydrogeological setting). For this reason, we assessed the interacting controls of hydrogeological setting and burn severity on post-fire moss water availability in three burned, Sphagnum -dominated peatlands in Alberta’s Boreal Plains. At all sites, variation in burn severity resulted in a dichotomy between post-fire surface covers that: (1) exhibited low water availability, regardless of WT position, and had minimal ( i.e. lightly burned feather mosses and severely burned Sphagnum fuscum ) or (2) exhibited high water availability, depending on WT position, and had substantial (>50%) moss re-establishment ( i.e. lightly burned S. fuscum and where depth of burn was >0.05 m). Notably, hydrogeological setting influenced the spatial coverage of these post-fire surface covers by influencing pre-fire WTs and stand characteristics ( e.g. , shading). Because feather moss cover is controlled by tree shading, lightly burned feather mosses were ubiquitous (>25%) in drier peatlands (deeper pre-fire WTs) that were densely treed and had little connection to large groundwater flow systems. Moreover, hydrogeological setting also controlled post-fire WT positions, thereby affecting moss re-establishment in post-fire surface covers that were dependent on WT position ( e.g. , lightly burned S. fuscum ). Accordingly, higher recolonization rates were observed in a peatland located in a groundwater flow through system that had a shallow post-fire WT. Therefore, we argue that hydrogeological setting influences post-fire recovery in two ways: (1) by influencing vegetation structure prior to wildfire, thereby controlling the coverage of post-fire surface covers and (2) by influencing post-fire WT positions. These results suggest that post-fire moss recovery in peatlands isolated from groundwater flow systems may be particularly susceptible to droughts and future climate change.

Burn severity alters peatland moss water availability: implications for post‐fire recovery

AbstractWildfire is the largest disturbance affecting northern peatlands; however, little is known about how burn severity (organic soil depth of burn) alters post‐fire hydrological conditions that control the recovery of keystone peatland mosses (i.e. Sphagnum). For this reason, we assessed the impact of burn severity on moss water availability by measuring soil tension (Ψ) and surface volumetric moisture content (θ) in burned and unburned portions of a peatland complex 2 years after fire. We found that both high and low burn severity decreased post‐fire water availability by altering peat hydrophysical properties (moisture retention and water repellency). Locations covered by Sphagnum fuscum prior to fire exhibited a decreasing post‐fire water availability with an increasing burn severity. In contrast, the lowest water availability (Ψ > 400 cm, θ < 0·02) was observed in feather mosses that underwent low burn severity (residual branches identifiable). Deep burning (>0·20 m) in peatland margins and burn depths >0·05 m in the middle of the peatland exhibited the highest water availability (Ψ < 60 cm). Locations with low surface θ and high Ψ, notably feather mosses undergoing low burn severity, exhibited minimal moss recolonization. Such areas dominate post‐fire surface cover (~40%) within late successional (mature) peatlands or peatlands located in dry hydrological settings. We argue that such environments are under‐represented in conceptual models of post‐fire recovery. A new conceptual model is proposed in which (1) deep burning is counterbalanced by rapid recolonization and (2) pre‐fire species interact with burn severity to produce substantial lags in post‐fire moss recovery. Copyright © 2015 John Wiley & Sons, Ltd.

Role of morphological structure and layering ofSphagnumandTomenthypnummosses on moss productivity and evaporation rates

Goetz, J. D. and Price, J. S. 2015. Role of morphological structure and layering of Sphagnum and Tomenthypnum mosses on moss productivity and evaporation rates. Can. J. Soil Sci. 95: 109–124. Morphological structures of peatland mosses control moss water relations and the rate of water loss by drainage and evaporation, thus influencing their physiological functions. While many of these mechanisms are understood for Sphagnum mosses, there is a limited understanding of how these processes operate in Tomenthypnum nitens, a dominant brown moss species in northern rich fens. This study contrasts how different hydrophysical characteristics of Tomenthypnum and Sphagnum species affect capillary water flow that supports evaporation and productivity. Laboratory investigations indicate that volumetric water content (θ), gross ecosystem productivity, and evaporation decreased with water table depth for both mosses, with Sphagnum capitula retaining 10–20% more water (θ range of 0.18–0.32 cm3cm−3) than Tomenthypnum (0.07−0.16 cm3cm−3). Despite lower θ and a smaller fraction of pores between 66 and 661 µm to retain water within the Tomenthypnum structure (10%) compared with Sphagnum (27%), both mosses had similar fractions of water conducting pore spaces and were able to maintain capillary rise throughout the experiment. While there was a larger difference in the bulk density and porosity of the Tomenthypnum moss compared with its underlying peat than there was in the Sphagnum profile, a layer of partially decomposed moss of intermediate properties was sufficient to provide a connection between the moss and peat under low water table conditions. In trying to characterize the soil-water pressure (ψ) in near-surface mosses of Tomenthypnum based on measurements of vapour pressure, we found disequilibrium conditions that severely underestimated ψ (i.e., very large negative pressures). It is this disequilibrium that drives evaporation and draws up capillary water to the moss surface for peatland–atmosphere carbon and water transfers.

Physiological and biochemical responses of Syntrichia caninervis at a snowfall event in different desert habitats

Aims Water is the most constraining factor to the growth of plants in arid and semiarid regions of China. Biological soil crusts(BSCs) develop well in Gurbantunggut Desert and Syntrichia caninervis is a dominant species in the moss crusts of this cold desert. Compared to other desert ecosystems, the Gurbantunggut desert is home to stable and abundant snow cover in winter. The moisturizing and warming effects of snow cover provide the desert mosses with optimal growth conditions. Our objective in this study was to determine how S. caninervis shoots utilize the special snow resources under different microhabitats in early winter. Methods The experiments were conducted from prior to the snowfall and until following the snow thawing at a long-term study site of the Gurbantunggut Desert. We measured the physiological and biochemical characteristics in S. caninervis in three habitats: the live shrub, the dead shrub, an exposed area. The shoot water content, chlorophyll fluorescence, proline content, soluble sugar content, soluble protein content, malonyldialdehyde(MDA) content, peroxidase(POD) and superoxide dismutase(SOD) activity were compared. Important findings The results showed that snowfall increased moss water content, the maximal photochemical efficiency of PSII(Fv/Fm), soluble sugar content, SOD and POD activity. The content of proline and MDA were reduced with snow melting. Microhabitats influenced the physiological characteristics in S. caninervis, with the effects varying with snowfall event. The water content and chlorophyll fluorescence activity were significantly higher in samples under the living shrub, while in the exposed area S. caninervis had lower water content and chlorophyll fluorescence activity regardless of the snowfall cover. These findings suggested that the S. caninervisplants under the loving shrub experienced the least stress and had the best physiological performance but weak resistance, and that those in exposed area were more stress tolerant and had poorer physiological performance. Following the snowfall, proline content, MDA content, POD and SOD activity all had significantly negative correlations with plant water content; whereas the soluble sugar and protein content displayed significantly positive correlations with plant water content. The results indicated that snowfall reduced the water stress in S. caninervis, and enhanced their physiological performance and photosynthesis, with the effects being facilitated by the low temperature of the early winter.

Simulation of six years of carbon fluxes for a sedge‐dominated oligotrophic minerogenic peatland in Northern Sweden using the McGill Wetland Model (MWM)

AbstractNorthern peatlands store ~30% of the global soil carbon, despite covering only 3% of the land. To understand the carbon balance of these systems and predict their response to changes in climate, robust and reliable models are needed. The McGill Wetland Model (MWM), originally developed to simulate the carbon dynamics of ombrotrophic bogs, was modified to simulate the CO2 biogeochemistry of sedge‐dominated oligotrophic minerogenic peatlands, a prominent peatland type in boreal and subarctic landscapes. Three modifications were implemented: (1) a function to describe the impact of soil moisture on the optimal gross primary production, (2) a scheme to partition the peat profile into oxic and anoxic compartments based on the “effective root depth” as a function of daily sedge net primary production, and (3) a function to describe the “fen” moss water dynamics. The modified MWM was evaluated using eddy‐covariance net ecosystem production (NEP) from Degero Stormyr in northern Sweden. The root mean square error for daily NEP was ~0.46 g C m−2 d−1, and the index of agreement was 84%. This model adequately captures the magnitude and direction of the CO2 fluxes and simulates the seasonal and inter‐annual variability reasonably well (r2 > 0.8). Sensitivity analysis confirms that specifically water table depth (WTD) and moss water content are key biogeochemical hydrology processes for the carbon biogeochemistry of a sedge‐dominated oligotrophic minerogenic peatland. An increase of WTD by 15 cm or air temperature by 3°C could decrease NEP by up to 200% and make the peatland become a source of CO2.

Temporal separation between CO2 assimilation and growth? Experimental and theoretical evidence from the desiccation‐tolerant moss Syntrichia ruralis

The extent of an external water layer around moss tissue influences CO(2) assimilation. Experiments on the desiccation-tolerant moss Syntrichia ruralis assessed the real-time dependence of the carbon and oxygen isotopic compositions of CO(2) and H(2)O in terms of moss water status and integrated isotope signals in cellulose. As external (capillary) water, and then mesophyll water, evaporated from moss tissue, assimilation rate, relative water content and the stable isotope composition of tissue water (δ(18)O(TW)), and the CO(2) and H(2)O fluxes, were analysed. After drying, carbon (δ(13)C(C)) and oxygen (δ(18)O(C)) cellulose compositions were determined. During desiccation, assimilation and (13)CO(2) discrimination increased to a maximum and then declined; δ(18)O(TW) increased progressively by 8‰, indicative of evaporative isotopic enrichment. Experimental and meteorological data were combined to predict tissue hydration dynamics over one growing season. Nonsteady-state model predictions of δ(18)O(TW) were consistent with instantaneous measurements. δ(13)C(C) values suggest that net assimilation occurs at 25% of maximum relative water content, while δ(18)O(C) data suggests that cellulose is synthesized during much higher relative water content conditions. This implies that carbon assimilation and cellulose synthesis (growth) may be temporally separated, with carbon reserves possibly contributing to desiccation tolerance and resumption of metabolism upon rehydration.

Modeling the effects of hydrology on gross primary productivity and net ecosystem productivity at Mer Bleue bog

[1] The ecosys model was applied to investigate the effects of water table and subsurface hydrology changes on carbon dioxide exchange at the ombrotrophic Mer Bleue peatland, Ontario, Canada. It was hypothesized that (1) water table drawdown would not affect vascular canopy water potential, hence vascular productivity, because roots would penetrate deeper to compensate for near‐surface dryness, (2) moss canopy water potential and productivity would be severely reduced because rhizoids occupy the uppermost peat that is subject to desiccation with water table decline, and (3) given that in a previous study of Mer Bleue, ecosystem respiration showed little sensitivity to water table drawdown, gross primary productivity would mainly determine the net ecosystem productivity through these vegetation–subsurface hydrology linkages. Model output was compared with literature reports and hourly eddy‐covariance measurements during 2000–2004. Our findings suggest that late‐summer water table drawdown in 2001 had only a minor impact on vascular canopy water potential but greatly impacted hummock moss water potential, where midday values declined to −250 MPa on average in the model. As a result, simulated moss productivity was reduced by half, which largely explained a reduction of 2–3 mmol CO2 m −2 s −1 in midday simulated and measurement‐derived gross primary productivity and an equivalent reduction in simulated and measured net ecosystem productivity. The water content of the near‐surface peat (top 5–10 cm) was found to be the most important driver of interannual variability of annual net ecosystem productivity through its effects on hummock moss productivity and on ecosystem respiration.

Measurement and modelling of bryophyte evaporation in a boreal forest chronosequence

AbstractThe effects of changing climate and disturbance on forest water cycling are not well understood. In particular, bryophytes contribute significantly to forest evapotranspiration in poorly drained boreal forests, but few studies have directly measured this flux and how it changes with stand age and soil drainage. We measured bryophyte evaporation (E) in the field (in Canadian Picea mariana forests of varying ages and soil drainages) and under controlled laboratory conditions, and modelled daily E using site‐specific meteorological data to drive a Penman–Monteith‐based model. Field measurements of E averaged 0·37 mm day−1 and ranged from 0·03 (Pleurozium schreberii in a 77‐year‐old dry stand) to 1·43 mm day−1 (Sphagnum riparium in a 43‐year‐old bog). In the laboratory, moss canopy resistance (which ranged from ∼0 to 1500 s m−1) was constant until a moss water content of ∼6 g g−1 and then climbed sharply with further drying; unexpectedly, no difference was observed between the three moss groups (feather mosses, hollow mosses and hummock mosses) tested. Modelled annual E ranged from 0·4 mm day−1, in the well‐drained stands, to ∼1 mm day−1 in the 43‐year‐old bog. The Penman–Monteith modelling approach used was relatively insensitive to most parameters but only explained 35% of the variability in field measurements. Bryophyte E was greater in bogs than in upland stands, was driven by low‐lying mosses and varied with stand age only in the poorly drained stands; this suggests that bryophytes may provide a buffering effect to fire‐driven changes in tree transpiration. Copyright © 2010 John Wiley & Sons, Ltd.

The response of carbon dioxide exchange to manipulations of Sphagnum water content in an ombrotrophic bog

AbstractSphagnum mosses contribute to the long‐term carbon sequestration of many northern peatlands. Variability in both Sphagnum and peatland CO2 exchange is strongly influenced by water availability, but there is limited work examining the links between these relationships, particularly in a field setting. In this study, the effects of varying moss water content (WC), through precipitation exclusion (PE) and water addition (WA) treatments, on net ecosystem CO2 exchange (NEE) and component fluxes were assessed during a single growing season at Mer Bleue bog, a temperate ombrotrophic peatland. CO2 exchange by Sphagnum, vascular plants, and the total ecosystem were measured in situ using chambers. On average, the hummock species of Sphagnum dominant at the site maintained WCs within the optimal range for photosynthesis in all treatments and no treatment effect on CO2 exchange was observed. However, in a few samples associated with below optimal WCs, Sphagnum photosynthesis was reduced. Water table (WT) depth and direct precipitation were both important controls on Sphagnum WC, suggesting that frequent small rain events may be important in maintaining Sphagnum WC. This study only explored one variable associated with drought conditions (i.e. water availability through intercepted precipitation). Consequently, further study is necessary to assess the relative importance of deep WT positions and high temperatures on moss WC. Nevertheless, the results of this study suggest that decreased Sphagnum photosynthesis has the potential to influence peatland CO2 uptake at Mer Bleue in drought years, but only if moss WC is reduced below the optimal range. Copyright © 2010 John Wiley & Sons, Ltd.