Читать книгу Wetland Carbon and Environmental Management - Группа авторов - Страница 50

Primary production in wetlands can rival that in other highly productive systems such as tropical rain forests and agricultural systems (Millennium Ecosystem Assessment, 2005). Despite this generalization, there is considerable spatial and temporal variability in rates of primary productivity – both between and within wetlands – that is driven by factors including vegetation type, hydrology, climate, soil properties, and water quality. We focus here on production by higher plants but recognize that algal production can be substantial in some systems (e.g., Tobias & Neubauer, 2019 and references therein). Across a wetland landscape, spatial patchiness in vegetation assemblages can lead to greater temporal evenness in ecosystem carbon inputs compared to a system with more homogeneous vegetation (Korrensalo et al., 2020). Spatial variations in vegetation type can also influence carbon preservation since the chemistry of organic matter added to the soil varies with plant species (Belyea, 1996; Dunn et al., 2016; Kögel‐Knabner, 2002). Regular hydrologic pulsing (e.g., tidal rhythms, seasonal river flooding) enhances productivity versus wetlands with stagnant water or continuous deep flooding (Brinson et al., 1981; Odum et al., 1995). Interannual variations in sea level cause corresponding changes in salt marsh plant productivity (Morris et al., 2002). Vegetation productivity and species composition respond to climate over both short and long periods (e.g., Cavanaugh et al., 2014; Feurdean et al., 2019; Johnson et al., 2005; Mendelssohn & Morris, 2000). Rising atmospheric CO₂ levels increase production rates of C3 wetland plants but not C4 plants (Caplan et al., 2015; Curtis et al., 1989; Fenner et al., 2007). This generalization is supported by wetland studies, but it is worth noting that C4 plants can show positive growth responses, albeit smaller responses than are seen in C3 plants (Ainsworth & Long, 2005; B. G. Drake, 2014; Wand et al., 1999). Increasing salinity reduces plant productivity (Sutter et al., 2014), even in plants that are adapted to growing in saline conditions (Mendelssohn & Morris, 2000), although this may be a transient response at the ecosystem scale if the plant assemblage shifts to become dominated by salt‐tolerant plants (Herbert et al., 2015). Although wetlands are efficient at recycling inorganic nutrients (Hopkinson, 1992; Neubauer, Anderson et al., 2005), primary production often increases with allochthonous nutrient inputs (Brantley et al., 2008; Morris et al., 2002; Thormann & Bayley, 1997). Soil pH can influence plant productivity and community composition, especially in highly acidic conditions (Chapin et al., 2004; P. H. Glaser et al., 1990; MacCarthy & Davey, 1976). Interactions between these factors are common (e.g., Erickson et al., 2007; Langley & Megonigal, 2010), but discussing them is beyond the scope of this chapter.