DOI: 10.5061/dryad.0000000bm
title: Data from: No slowdown of growing season extension with warming in a permafrost-affected meadow on the Tibetan Plateau

description: The Tibetan Plateau holds the world’s largest alpine permafrost and is
 undergoing  an acceleration of warming. Phenological shifts over
 alpine permafrost in a warmer world have been little studied and are
 greatly underrepresented in current syntheses. Here, we conducted seasonal
 and gradient temperature-controlled experiments in a permafrost-affected
 meadow to evaluate how warming drives shifts in spring and autumn
 phenology, and associated growing-season length at both community and
 species levels. Our results showed that there is no sign of
 slowdown in spring advance with warming under a higher year-around warming
 treatment, aligning with a future medium warming scenario. This finding
 can be attributed to the possibility that winter warming is insufficient
 to reduce chilling accumulation, which would not delay spring phenology
 and then lead to a non-slowdown in spring phenological advancement.
 Although spring advance led to an advance in autumn senescence according
 to spring-only warming experiments, the advance could not offset the delay
 due to concurrent warming. As a result, year-around warming
 significantly delayed autumn senescence, although there was a deceleration
 in delay with warming under high temperature treatment than under the low
 one. Taken together, there is no slowdown in an extension of growing
 season length with warming under a higher year-around warming treatment,
 with an increase of length by 9 and 21 days at the end of this century
 under a CO2 stabilization and medium warming scenarios,
 respectively. Our results suggest that a continued growing season
 extension at least under the medium warming scenario would help
 permafrost-affected meadow ecosystems to mitigate permafrost carbon
 release on the Tibetan Plateau.
description: <strong>Experimental design</strong>
 The manipulative warming experimental platform in typical
 permafrost-affected region was established in April 2018. Hexagonal
 open-top warming chambers (OTCs), which were used extensively in the
 International Tundra Experiment (Wahren et al., 2013), were adopted to
 simulate the effect of warming on ecosystems. For the low warming
 gradient, the OTCs are 1.3 m in diameter at the base, 1.1 m in diameter at
 the top, and 0.4 m high. For the high warming gradient, the OTCs are 1.3 m
 in diameter at the base, 0.8 m in diameter at the top, and 0.8 m high
  (Figure S2). All chambers use the same light panels with 8mm thick and
 the light transmittance rate &gt; 95%. There were
 three warming treatments in our experiment: spring warming (from 10th
 February to 10th May), winter warming (from 10th November to 10th
 February) and year-round warming (throughout the whole year), each warming
 treatment set two warming gradient (40cm and 80cm height OTC,
 respectively) and four replicates. In total, 28 plots (4 replicates × 2
 levels × 3 treatments + 4 control replicates) were set up to explore the
 impact of seasonal warming on the sequence of phenological
 events. In addition, we also set up an active infrared
 warming experiment started in the year 2021 to explore the response of
 ecosystem dynamics to a gradient of warming. Specifically, it consists of
 the control and three warming treatments (constant warming of 1, 2 and 4℃
 with respect to the control), each with four replicates. Here we used
 ceramic heating elements (1000W, 240V, Campbell Scientific, Logan, USA) to
 produce and emit infrared radiation that could transfer energy from the
 infrared source to plots. For each plot, three stainless steel posts were
 anchored about 30 cm into the ground and three crossbars were then
 attached to the posts at a height of 1.6 m above the ground. The ceramic
 heating elements were bolted to the crossbars along the 1.6 m side, and
 sixteen triangular plots were then set up. The dummy heaters with the same
 shape and size were set up in control plots to mimic any possible
 infrastructure impact of infrared warming systems. We separated adjacent
 plots using a buffer zone of around 5-10 m to avoid interferences, and
 used a Proportional-Integral-Derivative control system (Campbell
 Scientific, Logan, USA) to ensure an accurate control of pre-set warming
 magnitude over plots (Kimball et al., 2008). This active warming system
 was deployed on the same site, given that passive warming systems such as
 OTCs were often criticized for the following reasons. First, OTCs often
 reduced soil moisture by passively heating a small vegetation plot by
 capturing more solar radiation and intercepting more rainfall events,
 which would potentially bias phenological responses to warming. Second,
 OTCs might act as barriers to wind flow and pollinator movement (Dong et
 al., 2023), although some studies found no significant effect of OTC
 installation on insect flower visitors (Robinson et al., 2018). Third, in
 contrast to active warming system that has a uniform warming magnitude on
 ecosystems, the impact of OTC on the magnitude of warming varies
 seasonally, with a lower magnitude in summer and higher ones during winter
 and spring seasons on our permafrost-affected site.
 <strong>Manual phenological
 observations</strong> Phenological events were
 consecutively monitored for the three years (2018–2020) at both community
 and species levels with 2~3 times per week interval depend on weather
 conditions. For community phenology observation, we set up in situ and
 permanent quadrat (1×1 m<sup>2</sup>) in each chamber, then
 meshed the quadrat into 100 cross points to record the individual
 phenological status under each projection of the cross points. Here we
 defined two threshold (10% and 90%, respectively) to identify the green up
 and green down days of community (Chen et al., 2022; Li et al., 2016; Meng
 et al., 2017). For instance, the start of the growing season (SOS) in
 community level is defined as 10% individuals at least under the cross
 point turn green, while the end of growing season in community level is
 defined as more than 90% individuals under the cross point into complete
 senescence and highly dehydrated. The start and the end of reproductive
 season in community level are defined as the date of 10% individuals turn
 into first flowering (FF) and 90% individuals turn into first fruit set
 (FFS), respectively.     For species level phenology
 observation, eight native perennial species which maximally represented
 the plant community assemble is recorded during the study period. These
 species accounted for 86.89% and 83.26% of the relative contributions to
 coverage and community biomass, based on their leaf out time, they were
 classified into three functional groups: early spring, mid spring and late
 spring species (Table 2). The intermediate date between first recorded
 date and the date of the preceding survey when the event was not recorded
 as the start date, and vice versa for determining the end date. For
 example, if the initial observation of leaf-out occurred on 26 April, and
 the preceding survey on 22 April did not record this event, then the
 estimated leaf-out date would be 24 April, which is the midpoint between
 the two dates (Li et al., 2016). The duration of each phenological event
 was the number of days between the start and ending date. Here the growing
 season was defined as the period from leaf onset to complete leaf
 senescence, while the reproductive season was defined as the interval from
 the first flowering to first fruit set. Based on
 previous study (Li et al., 2016; Meng et al., 2017) and well-known BBCH
 (Biologische Bundesanstalt, Bundessortenamt und CHemische Industrie)
 guidance (Meier et al., 2009), we selected 7 sequential and hierarchical
 phenological events in monitoring (Table 1). Because of low growing season
 temperature and rare pollinators, the flowering rate of native species is
 relatively low, most species also reproduce clonally (<em>Lagotis
 glauca Gaertn</em> for instance), in order to ensure the quality of
 phenological monitoring, more than 10 individuals for each species were
 marked in previous year. Once flower buds were noticed, the individual
 will be monitored as follows, if the individual fails to enter the
 reproductive phase, we choose another individual in monitoring, the data
 was averaged of all the selected individuals for each species we
 choose. In addition, air temperature near soil surface,
 soil moisture and temperature at 10 cm depth were recorded at an interval
 of 1 min using Decagon 5TM sensors (Decagon Devices, Pullman, Washington,
 USA). The logger auto calculated and saved the data on 30-minute averages
 across the whole year, and three replicates were designed for each
 treatment in this study. Mean annual solar radiation data are derived from
 the WorldClim Version 2.0 dataset (www.worldclim.org). For each phenological event at both community and species levels, its temperature sensitivity is calculated as the difference of phenological date to that of air temperatures between control and treatment plots (Δdays ℃<sup>-1</sup>). In addition, for a given phenological stage, we also computed phenological niche breadth as the length between the earliest species to that of the latest species in community.
description: # Data from: No slowdown of growing season extension with warming in a
 permafrost-affected meadow on the Tibetan Plateau ## Description of the
 data and file structure This ReadMe file accompanies the data for the
 article accepted by the Journal of Ecology. The data file is named
 (JEcol_Supplement_Data.xlsx). The data file contains three sheets:
 'Climate data','Community Phenology' and 'Species
 Phenology'. Abbreviations with simple description as follow, and a
 full description of these data can be found in sheet "ReadMe".
 **Worksheet：Climate data** This sheet contains environment conditons
 across the study years (more details see method): season: seasonal mean
 temperature in a specific season under each treatment, seasons were
 defined as belows: winter (from 10th November to 10th February); spring
 (from 10th February to 10th May); summer (from 10th May to 10th August);
 autumn (from 10 th August to Novermber). treatment: there are seven
 warming treatments in our experiment (more details see method): CK
 (control check); A40 (year-round warming with 40cm high OTCs); A80
 (year-round warming with 80cm high OTCs); S40 (spring warming with 40cm
 OTCs); S80 (spring warming with 80cm OTCs); W40 (winter warming with 40cm
 OTCs); W80 (winter warming with 80cm OTCs). soil temperature: soil
 temperature in the 10cm depth. air temperature: air temperature in the
 surface. **Worksheet：Community Phenology** year: study year (more details
 see method). treatment: there are seven warming treatments in our
 experiment (more details see method) across the three consecutive years:
 CK (control check); A40 (year-round warming with 40cm high OTCs); A80
 (year-round warming with 80cm high OTCs); S40 (spring warming with 40cm
 OTCs); S80 (spring warming with 80cm OTCs); W40 (winter warming with 40cm
 OTCs); W80 (winter warming with 80cm OTCs). plot: number of each plot,
 each treatment contains four replicates, there are 28 plots in total of
 our experiment. GUD: Green Up Date. GDD: Green Down Date. GSL: Growing
 Season Length. **Worksheet：Species Phenology** species: the phenological
 data of eight species were recorded in our experiment (more details see
 method). Kt: *Kobresia tibetica*; Kp: *Kobresia pygmaea*; Kh: *Kobresia
 humillis*; Ta: *Thalictrum alpinum*; As: *Astragalus saxorum*; Ps:
 *Potentilla saundersiana*; Lp: *Leontopodium pusillum*; Cc: *Carex
 coriophora*. treatment: there are seven warming treatments in our
 experiment (more details see method) across the three consecutive years:
 CK (control check); A40 (year-round warming with 40cm high OTCs); A80
 (year-round warming with 80cm high OTCs); S40 (spring warming with 40cm
 OTCs); S80 (spring warming with 80cm OTCs); W40 (winter warming with 40cm
 OTCs); W80 (winter warming with 80cm OTCs). stage: there are seven
 phenological stage recorded in our experiment (more details see method).
 LO: Leaf-out; FFB: First flower bud; FF: First flowering; FFS: First
 fruit-set; PFV: Post-fruit vegetation; FLS: First leaf senescence; CLS:
 Complete leaf senescence. date: the averaged julian day (day of year) for
 each specific phenological stage under different treatments.