DOI: 10.5061/dryad.b8gtht7cg
title: International biological flora: Nervilia nipponica

description: This account presents information on all aspects of the biology of
 Nervilia nipponica Makino (mukago-saishin) that are relevant to
 understanding its ecological characteristics and behaviour. The main
 topics are presented within the standard framework of the International
 Biological Flora: distribution, habitat, communities, responses to biotic
 factors, responses to the environment, structure and physiology,
 phenology, floral and seed characters, herbivores and disease, history,
 conservation and global heterogeneity. Nervilia nipponica is a small,
 stoloniferous, seasonally dormant herb that grows in the understorey of
 evergreen forests in the humid subtropical zone of central and western
 Japan, with a few outlying populations on Jeju Island in South Korea. Its
 northern extent is defined by the 0ºC winter isotherm, and its occurrence
 is also limited by site aspect and incline. It is a weak competitor that
 occupies species-poor microsites in which bare ground and leaf litter
 predominate. Plant numbers tend to decline as percentage ground cover of
 surrounding understorey vegetation increases. The inflorescence sprouts
 from a short-lived, subterranean tuber in late spring and leaf-flush
 occurs after fruit-set. However, most tubers do not flower in any one
 annual growth cycle. Long-term monitoring of individually marked plants
 suggests that tubers are resource-limited and that flowering constrains
 future genet growth. Nervilia nipponica is exclusively autogamous and has
 a strong capacity for vegetative propagation. The species is genetically
 depauperate but exhibits significant differentiation between populations,
 which comprise clonal clusters in phalanx formation. The level of
 mycorrhizal infection differs between plant parts and through successive
 phenological stages. Stable isotope signatures indicate that the species
 is partially mycoheterotrophic, with fungal partners supporting growth
 particularly at lower light intensities. Despite this, falling light
 availability associated with forest succession can lead to population
 decline. Populations tend to be small and prone to extirpation, but the
 species is probably under-recorded as a result of its ephemeral emergence
 above ground and inconspicuous habit. Management interventions likely to
 benefit the species at the site level include thinning dense forest canopy
 and removing encroaching ground cover.
description: Number of emergent plants of Nervilia nipponica was
 recorded in each of 27 quadrats in August 2004 and again in August 2007.
 The percentage ground cover of understorey vegetation up to height 2 m was
 estimated on both dates. The change in number of emergent plants over the
 study period was correlated to change in percentage ground
 cover. All emergent plants
 occurring within a fixed plot measuring 10 x 14 m were marked and their
 locations were recorded as x and y coordinates to the nearest cm every
 year in late July to mid-August from 2003 to 2012. Observed and expected
 nearest neighbour distances were calculated and significance was measured
 using a Monte Carlo test in Point Pattern Analysis (PPA) software, which
 compares the complete distribution function of observed distances between
 nearest neighbours, F(di ≤ r), with the distribution function expected
 under a null hypothesis of complete spatial randomness, P(di ≤
 r). All emergent plants
 occurring within a fixed plot measuring 10 x 14 m were marked and
 monitored three times through each growing season (during the flowering,
 fruiting and leafing phases) for 10 years. Unmarked plants were labelled
 and incorporated into the record of the population’s demographic behaviour
 as they appeared. The pattern of emergence was inferred for each
 individual plant for the 10-year period.
 Five plants were excavated from each of two
 populations (sites T1 and T2) in Tochigi Prefecture and their
 photosynthetic capacity was measured using a Li-6400 infrared gas exchange
 analyser (Li-Cor, Lincoln, Nebraska, USA). Net carbon assimilation rate (g
 glucose m-2 day-1) was calculated by aggregating the instantaneous net
 assimilation rate of the leaves (Anet, μmol CO2 m-2 s-1) and converting
 this to the mass of glucose (g mol-1) contributing to new biomass growth.
 Photosynthetic carbon gain calculated in this way was compared to measured
 carbon gain, as inferred from the difference in dry mass in cohorts of 4–5
 plants harvested at monthly intervals (July, August, September and
 October) over three growing seasons (2014–2016). Each plant was divided
 into leaf and petiole, stolon and tubers, leaf area was measured, and all
 plant parts were oven-dried and weighed. Carbon gain dependency was
 defined as the ratio of calculated biomass gain from photosynthesis
 (derived from photosynthetic light-response curves using PAR data and the
 measured photosynthetic capacity of N. nipponica) to observed biomass gain
 (derived from mean dry mass differential from first to last sampling).
 Stable 13C and 15N isotope abundances were determined in N. nipponica and
 in a range of other co-occurring understorey herbs, including both
 chlorophyllous and achlorophyllous species at both sites in Tochigi
 Prefecture during July to September in 2014, to estimate the percentage
 carbon and nitrogen gain from fungal partners, following the methodology
 of Gebauer & Meyer (2003).
description: As explained in appended README file