Effects of soil freezing on fine roots in a northern hardwood forest (original) (raw)
Related papers
Soil freezing alters fine root dynamics in a northern hardwood forest
2001
The retention of nutrients within an ecosystem depends on temporal and spatial synchrony between nutrient availability and nutrient uptake, and disruption of fine root processes can have dramatic impacts on nutrient retention within forest ecosystems. There is increasing evidence that overwinter climate can influence biogeochemical cycling belowground, perhaps by disrupting this synchrony. In this study, we experimentally reduced snow accumulation in northern hardwood forest plots to examine the effects of soil freezing on the dynamics of fine roots (< 1 mm diameter) measured using minirhizotrons. Snow removal treatment during the relatively mild winters of 1997-1998 and 1998-1999 induced mild freezing temperatures (to −4 • C) lasting approximately three months at shallow soil depths (to −30 cm) in sugar maple and yellow birch stands. This treatment resulted in elevated overwinter fine root mortality in treated compared to reference plots of both species, and led to an earlier peak in fine root production during the subsequent growing season. These shifts in fine root dynamics increased fine root turnover but were not large enough to significantly alter fine root biomass. No differences in morality response were found between species. Laboratory tests on potted tree seedlings exposed to controlled freezing regimes confirmed that mild freezing temperatures (to −5 • C) were insufficient to directly injure winter-hardened fine roots of these species, suggesting that the marked response recorded in our forest plots was caused indirectly by mechanical damage to roots in frozen soil. Elevated fine root necromass in treated plots decomposed quickly, and may have contributed an excess flux of about 0.5 g N/m 2 ·yr, which is substantial relative to measurements of N fluxes from these plots. Our results suggest elevated overwinter mortality temporarily reduced fine root length in treatment plots and reduced plant uptake, thereby disrupting the temporal synchrony between nutrient availability and uptake and enhancing rates of nitrification. Increased frequency of soil freezing events, as may occur with global change, could alter fine root dynamics within the northern hardwood forest disrupting the normally tight coupling between nutrient mineralization and uptake.
Oecologia, 2012
Due to projected increases in winter air temperatures in the northeastern USA over the next 100 years, the snowpack is expected to decrease in depth and duration, thereby increasing soil exposure to freezing air temperatures. To evaluate the potential physiological responses of sugar maple (Acer saccharum Marsh.) to a reduced snowpack, we measured root injury, foliar cation and carbohydrate concentrations, woody shoot carbohydrate levels, and terminal woody shoot lengths of trees in a snow manipulation experiment in New Hampshire, USA. Snow was removed from treatment plots for the first 6 weeks of winter for two consecutive years, resulting in lower soil temperatures to a depth of 50 cm for both winters compared to reference plots with an undisturbed snowpack. Visibly uninjured roots from trees in the snow removal plots had significantly higher (but sub-lethal) levels of relative electrolyte leakage than trees in the reference plots. Foliar calcium: aluminum (Al) molar ratios were significantly lower, and Al concentrations were significantly higher, in trees from snow removal plots than trees from reference plots. Snow removal also reduced terminal shoot growth and increased foliar starch concentrations. Our results are consistent with previous research implicating soil freezing as a cause of soil acidification that leads to soil cation imbalances, but are the first to show that this translates into altered foliar cation pools, and changes in soluble and structural carbon pools in trees. Increased soil freezing due to a reduced snowpack could exacerbate soil cation imbalances already caused by acidic deposition, and have widespread implications for forest health in the northeastern USA. Keywords Soil freezing Á Root injury Á Woody shoot growth Á Carbohydrate and cation concentrations Á Acer saccharum 100 years in the northeastern USA, the number of days each year with snow on the ground is projected to decrease Communicated by Zoe Cardon.
To Decreased Root Uptake in a Northern Hardwood
2013
The depth and duration of snow pack is declining in the northeastern United States as a result of warming air temperatures. Since snow insulates soil, a decreased snow pack can increase the frequency of soil freezing, which has been shown to have important biogeochemical implications. One of the most notable effects of soil freezing is increased inorganic nitrogen losses from soil during the following growing season. Decreased nitrogen retention is thought to be due to reduced root uptake, but has not yet been measured directly. We conducted a 2-year snow-removal experiment at Hubbard Brook Experimental Forest in New Hampshire, USA to determine the effects of soil freezing on root uptake and leaching of inorganic nitrogen simultaneously. Snow removal significantly increased the depth of maximal soil frost by 37.2 and 39.5 cm in the first and second winters, respectively (P < 0.001
Global Change Biology, 2014
The depth and duration of snow pack is declining in the northeastern United States as a result of warming air temperatures. Since snow insulates soil, a decreased snow pack can increase the frequency of soil freezing, which has been shown to have important biogeochemical implications. One of the most notable effects of soil freezing is increased inorganic nitrogen losses from soil during the following growing season. Decreased nitrogen retention is thought to be due to reduced root uptake, but has not yet been measured directly. We conducted a 2-year snow-removal experiment at Hubbard Brook Experimental Forest in New Hampshire, USA to determine the effects of soil freezing on root uptake and leaching of inorganic nitrogen simultaneously. Snow removal significantly increased the depth of maximal soil frost by 37.2 and 39.5 cm in the first and second winters, respectively (P < 0.001
Colder soils in a warmer world: a snow manipulation study in a northern hardwood forest ecosystem
2001
In this special section of Biogeochemistry, we present results from a snow manipulation experiment in the northern hardwood forest ecosystem at the Hubbard Brook Experimental Forest in the White Mountains of New Hampshire, U.S.A. Snow is important as an insulator of forest soils. Later development of snowpacks, as may occur in a warmer climate, may result in increases in soil freezing (i.e. colder soils in a warmer world) and could cause changes in fine root and microbial mortality, hydrologic and gaseous losses of nitrogen (N), and the acid-base status of drainage water. In our study, we kept soils snow free by shoveling until early February during the mild winters of 1997/1998 and 1998/1999. The treatment produced mild, but persistent soil freezing and induced surprisingly significant effects on root mortality, soil nitrate (NO − 3 ) levels and hydrologic fluxes of C, N and P. In this special section we present four papers addressing, (1) soil temperature and moisture response to our snow manipulation treatment Hardy et al.), (2) the response of fine root dynamics to treatment (Tierney et al.), (3) the response of soil inorganic N levels, in situ N mineralization and nitrification, denitrification and microbial biomass to the treatment (Groffman et al.) and (4) soil solution concentrations and fluxes of C, N and P (Fitzhugh et al.). In this introductory paper we: (1) review the literature on snow effects on forest biogeochemistry, (2) introduce our manipulation experiment and (3) summarize the results presented in the other papers in this issue.
Root mechanical properties related to disturbed and stressed habitats in the Arctic
New Phytologist, 1992
Various mechanical and architectural properties of roots were measured on plants characteristic of different levels of soil disturbance associated with frost-heave cycles on sorted polygons in Swedish Lapland: one of these measures, resilience, has not, apparently, been recorded previously in literature. Some roots were sampled from species which occurred on both disturbed and stable soils.
Delayed soil thawing affects root and shoot functioning and growth in Scots pine
Tree Physiology, 2008
In boreal regions, soil can remain frozen after the start of the growing season. We compared relationships between root characteristics and water relations in Scots pine (Pinus sylvestris L.) saplings subjected to soil frost treatments before and during the first week of the growing period in a controlled environment experiment. Delayed soil thawing delayed the onset of sap flow or totally blocked it if soil thawing lagged the start of the growing period by 7 days. This effect was reflected in the electrical impedance of needles and trunks and in the relative electrolyte leakage of needles. Prolonged soil frost reduced or completely inhibited root growth. In unfrozen soil, limited trunk sap flow was observed despite unfavorable aboveground growing conditions (low temperature, low irradiance, short photoperiod). Following the earliest soil thaw, sap flow varied during the growing season, depending on light and temperature conditions, phenological stage of the plant and the amount of live needles in the canopy. The results suggest that delayed soil thawing can reduce tree growth, and if prolonged, it can be lethal.
Canadian Journal of Forest Research, 2002
The effects of induced root freezing injury on 2+0 white spruce (Picea glauca (Moench) Voss), black spruce (Picea mariana (Mill.) BSP), and jack pine (Pinus banksiana Lamb.) seedlings were studied. Hardened seedlings were exposed to freezing during the fall and cold stored until planting. Seedlings were planted in spring on two field sites with different soil moisture levels (wet or dry). Seedling morphology and physiology were measured periodically during the first growing season, and mortality was evaluated at the end of the season. With the exception of June measurements on the wet site, where daytime water potential fell as low as-2.0 MPa, root damage did not seriously affect shoot water potential. Generally, stomatal conductance decreased with increasing root damage. Net photosynthesis on both sites decreased between 22 and 39% with increasing root damage. Root damage did not affect the ratio of intercellular to ambient CO 2 concentration. As well, reductions in the nitrogen concentration of current-year foliage with increasing root damage were observed, suggesting that the observed reductions in net photosynthesis were caused by nonstomatal factors. Root growth was greater on the wet site than on the dry site, particularly between August and October, when mean soil minimum temperatures were lower on the dry site. On both sites, aerial dry mass was only slightly affected by root damage in July and August, but the effect of damage became more pronounced in October on the wet site. Black spruce and white spruce seedling mortality began being affected when approximately 50% of the root systems were damaged, while jack pine mortality was affected starting at 40% damage. Root damage levels of 50% caused 2.0 and 1.5 cm reductions in annual height increment of white spruce and black spruce, respectively, and 40% damage caused a reduction of 1.0 cm in annual height increment of jack pine. Résumé : Les effets des dommages racinaires causés par le gel ont été étudiés chez des semis 2+0 d'épinette blanche (Picea glauca (Moench) Voss), d'épinette noire (Picea mariana (Mill.) BSP) et de pin gris (Pinus banksiana Lamb.). Des semis endurcis ont été exposés au gel durant l'automne avant d'être entreposés en chambre froide. Au printemps suivant, ces semis ont été plantés sur deux sites ayant des teneurs en eau du sol distinctes (mouilleux et sec). La morphologie et la physiologie des semis ont été mesurées périodiquement durant la première saison de croissance. La mortalité a été évaluée à la fin de la saison. À l'exception des mesures prises sur le site mouilleux en juin, où des valeurs de-2,0 MPa ont été observées, les dommages racinaires n'ont pas sérieusement affecté le potentiel hydrique du xylème. Généralement, la conductance stomatique a diminué avec l'augmentation des dommages. Des diminutions de 22 à 39% de la photosynthèse nette ont été observées sur les deux sites avec l'augmentation des dommages. Les dommages aux racines n'ont pas affecté le ratio de la concentration intercellulaire en CO 2 sur la concentration ambiante en CO 2 , mais des réductions de la teneur en azote du feuillage de l'année courante ont été observées, indiquant que les diminutions de la photosynthèse nette ont été causées par des facteurs non-stomatiques. La croissance racinaire a été plus élevée sur le site mouilleux, particulièrement entre août et octobre alors que les températures minimales moyennes du sol ont été plus basses sur le site sec. Sur les deux sites, l'effet des dommages racinaires sur la biomasse aérienne a été léger en juillet et en août, mais s'est accentué en octobre sur le site mouilleux. Pour l'épinette noire et l'épinette blanche, la mortalité a été perceptible lorsque environ 50% du système racinaire était endommagé. Pour le pin gris, la mortalité a été perceptible à partir de 40% de dommages. Des dommages racinaires de 50% ont causé des réductions de croissance en hauteur de 2,0 et 1,5 cm respectivement pour l'épinette blanche et l'épinette noire. Pour le pin gris, des dommages racinaires de 40% ont provoqué une réduction de croissance en hauteur de 1,0 cm. Dumais et al.
Environmental control of fine root dynamics in a northern hardwood forest
Global Change Biology, 2003
Understanding how exogenous and endogenous factors control the distribution, production and mortality of fine roots is fundamental to assessing the implications of global change, yet our knowledge of control over fine root dynamics remains rudimentary. To improve understanding of these processes, the present study developed regression relationships between environmental variables and fine root dynamics within a northern hardwood forest in New Hampshire, USA, which was experimentally manipulated with a snow removal treatment. Fine roots (< 1 mm diameter) were observed using minirhizotrons for 2 years in sugar maple and yellow birch stands and analyzed in relation to temperature, water and nutrient availability. Fine root dynamics at this site fluctuated seasonally, with growth and mortality peaking during warmer months. Monthly fine root production was strongly associated with mean monthly air temperature and neither soil moisture nor nutrient availability added additional predictive power to this relationship. This relationship exhibited a seasonal temperature hysteresis, which was altered by snow removal treatment. These results suggest that both exogenous and endogenous cues may be important in controlling fine root growth in this system. Proportional fine root mortality was directly associated with mean monthly soil temperature, and proportional fine root mortality during the over-winter interval was strongly related to whether the soil froze. The strong relationship between fine root production and air temperature reported herein contrasts with findings from some hardwood forest sites and indicates that controls on fine root dynamics vary geographically. Future research must more clearly distinguish between endogenous and exogenous control over fine root dynamics in various ecosystems.